YEAR I- SE MESTER I
THEORY
Version 1:
December 2008
TABLE OF CONTENTS
Topic Page
What is a computer? -- - - - - - - 1
The Basic Function
of a Computer - - - - 1
Main parts of a Personal Computer - - - - - 4
The System Unit - - - - - - 4
The System (Mother) Board - - - - - 4
The CPU (Central Processing Unit) - - - - 4
Memory RAM - - - - - - - 5
Memory ROM – BIOS - - - - - 5
What is a Peripheral Device? - - - - - 5
What are Input Devices? - -- - - - 5
What are Output Devices? - - - - - 6
Know how Computer Memory is Measured - - - - 9
Characteristics of Computers - - - - - - 10
The Five Generations of Computers - - - - - 11
First Generation –
1940 – 1956: Vacuum Tubes - - 11
Second Generation –
1956 – 1963: Transistors - - 11
Third Generation –
1964 – 1971: Integrated Circuit - 11
Fourth Generation –
1971 – Present: Microprocessors - 12
Fifth Generation – Present and Beyond: Artificial Intelligence 12
Brief History of Computers - - - - - - 13
Classes of Computers - - - - - - 22
Digital Computer - - - - - - 22
Analog Computer - - - - - - 22
Hybrid Computer - - - - - - 24
Classification of Input Devices - - - - - 26
Keyboards - - - - - - - 27
Pointing Devices - - - - - - 27
High-Degree of
Freedom Input Devices - - - 28
Composite Devices - - - - - 28
Audio Input Devices - - - - - - 29
Imaging and Video
Input Devices - - - - 29
Some Output Devices - - - - - - - 30
Visual Display Unit - - - - - 30
Speaker - - - - - - - 30
Printer - - - - - - - - 31
List of Graphical Output Devices - - - - - 31
Computer Storage - - - - - - - 32
Primary Storage - - - - - - 32
Secondary Storage - - - - - - 34
Purpose of Storage - - - - - - - 35
Hierarchy of Storage - - - - - - - 36
Characteristics of Storage - - - - - - 38
How Computers Work - - - - - - 40
Computer Software - - - - - - - 46
System Software - - - - - - 47
Operating System - - - - - - 47
The main Functions of Operating System - - - - 48
Types of Operating System - - - - - - 48
User Applications Software - - - - - - 49
Commercial Packages - - - - - - 50
Guideline for Acquisition of Application Software - - - 51
Social Implication of Computers on the Society - - - 51
The Office - - - - - - - 51
Manufacturing
Industry - - - - - 52
Health - - - - - - - - 52
Finance and
Commerce - - - - - 52
Military
Application - - - - - - 53
Education and
Training - - - - - 53
Computer as an Aid
to Lawyer - - - - 53
Data Processing Technique - - - - - - 53
Distributed Processing - - - - - - 54
Centralized System - - - - - - - 54
Data Communication and Networks - -- - - - 55
On-Line Data
Transmission - - - - - 57
Off-Line Data Communication - - - - 57
Elements of Data Communication - - - - - 57
Equipment/Components Required for Data Transmission - 57
Types of Transmission - - - - - - 58
Networks - - - - - - - - 58
Categories of Networks - - - - 59
Components of Network - - - - 59
Network Topologies - - - - - - 59
Internet Basics - - - - - - - 60
Benefits of
Internet Application - - - - 61
Uses of the
Internet - - - - - - 61
Microsoft Windows ‘95/98/me/XP - - - - - 62
Starting and Ending
Windows 95/98/me - - - 63
Your Desktop - - - - - - - 64
Working with a
Mouse - - - - - 65
Launching Programs - - - - - - 66
Using Help - - - - - - - 67
Multitasking - - - - - - - 69
Copy and Paste - - - - - - 70
Managing Files in Ms Windows - - - - - 70
Creating and Saving
a Document - - - - 72
Keyboard Shortcuts - - - -- - - 75
Backup - - - - - - - - - 76
What is a computer?
The term computer is obtained from the word compute. A
computer is an electronic device that inputs (takes in) facts (known as data),
and then processes (does something to or with) it. Afterwards it outputs, or
displays, the results for you to see.
Data is all kinds of facts, including,
pictures, letters, numbers, and sounds. There are two main parts of computers,
hardware and software. Hardware is all of the parts of the computer you can see
and touch. Software is the instructions that a computer uses to do what you ask
it to. Pieces of software are often called programs. The basic function
performed by a computer is the execution of a program.
Figure 1.1 – A Complete computer system
The Basic
Function of a Computer
 |
Many people mistakenly think that where the computer normally
displays things is the computer. This is not true. That is the monitor (see
Figure 1.2). The computer is usually a box (see Figure 1.3). Also, you may call
the whole assembly of all the hardware (the computer and the monitor, for
example) the computer.
Figure 1.2 - A Cathode Ray Tube (CRT) monitor
Figure 1.3 – The Computer (System Unit)
There are different styles of monitors. One of these is the one
already shown. It is called a CRT monitor. It takes more power than the
other popular kind, called LCDs (see Figure 1.4). However, CRT monitors
work faster, which makes them better for fast games because the movement will
blur less. LCDs are thinner than CRTs, but they are more expensive.
Figure 1.4 – A Liquid Crystal Display (LCD) Monitor
Monitors are only one way the computer can output information for
you to see. Another popular output device is called a printer (see
Figure 1. 5). Printers are used to put data on paper. This is called hard
copy, what monitors show is called soft copy. Computers can also
output sounds; this is also soft copy.
Figure 1.5 – A Printer
There are also different kinds of input hardware. The two most
important are the mouse and the keyboard. A mouse (Figure 1.6) is
used to move the cursor around the screen (monitor display). A
keyboard (see Figure 1.7) is used to enter (type) letters, numbers, and
other symbols into a computer.
Figure 1.6 - A Mouse
Figure 1.6 - A Keyboard
Computers store all data in binary code, which is a number
system that only uses ones and zeros. One digit in binary code is called a bit,
eight bits is called a byte. A byte is the amount of space one letter
takes up. However when letters are formatted specially they get bigger, and so
usually things on a computer are thousands of bytes in size.
There are many different kinds of computers. The ones that most
people use are called
Personal Computers (PCs). Smaller
computers that are about the size of a briefcase are called laptops or notebooks.
There are also much more powerful computers called mainframes that can
be as big as a room or a house!
Main Parts of a Personal Computer
The System Unit
·
The "system unit" is
the name given to the main PC box that houses the various elements that go
together to make up the PC. For instance within the system unit is the computer
system's motherboard, which contains all the main components, such as the CPU.
The system unit also houses items such as the hard disk, the floppy disk and
CD-ROM drives etc. System units come in two basic varieties, the tower version,
as illustrated, or a desktop version, which is designed to sit on your desk
with your monitor on top of the system unit.
The System (Mother) Board
·
The system (mother) board is
contained within your system unit and all the vital computer systems plug
directly into the system board. The CPU is normally housed on your system board
along with all the other electronic components. Other items such as the hard
disk are attached to the system board, either directly or via cables. These
boards are getting smaller and smaller as the components become more
integrated. If you open up a modern system you will find that it is mainly full
of air.
The CPU (Central Processing Unit)
·
The CPU is the brains within
your computer. It performs most of the calculations within the computer and is
responsible for the smooth running of your operating system (Microsoft Windows)
as well as your application programs, such as word-processors, spreadsheets and
databases. There is a small amount of memory associated with the CPU, which it
uses to perform these operations. It also accesses and uses the main memory
(RAM - Random Access Memory) within your computer. In many ways, the CPU is the
single most important item within your computer that governs the overall speed
of your computer. The CPU's speed is measured in MHz. This relates to the
frequency that the CPU runs at and the higher the MHz rating of your CPU the
faster your computer will run. To give you some indication of how PCs have
advanced over the years, the original IBM PC released in 1981 ran at less than
5 MHz while modern PCs can run at speeds well in excess of 2000 MHz. Note that
1000 MHz is the same a 1 GHz.
More information:
Intel: http://www.intel.com
AMD: http://www.amd.com
Cyrix: http://www.viatech.com
Intel: http://www.intel.com
AMD: http://www.amd.com
Cyrix: http://www.viatech.com
Memory RAM
·
Random Access Memory (RAM) is
the main 'working' memory used by the computer. When the operating system loads
from disk when you first switch on the computer, it is copied into RAM. The
original IBM PC could only use up to 640 KB of memory (just over half a
megabyte), whereas a modern computer can effectively house as much RAM as you
can afford to buy. Commonly modern computers are supplied with over 128 MB of
RAM. As a rough rule, a Microsoft Windows based computer will operate faster if
you install more RAM. When adverts refer to a computer having 128 Mbytes of
memory, it is this RAM that they are talking about. Data and programs stored in
RAM are volatile (i.e. the information is lost when you switch off the
computer).
Memory ROM-BIOS
·
The ROM-BIOS (Read Only Memory
- Basic Input Output System) chip is a special chip held on your computer's
system (mother) board. It contains software that is required to make your
computer work with your operating system, for instance it is responsible for
copying your operating system into RAM when you switch on your computer.
What is a peripheral device?
·
A peripheral device is any
device that you can attach to your computer. Thus, you could attach a scanner
or modem to the back of your system unit.
What are input devices?
·
Input devices allow you to
input information to the computer and include things such as the keyboard and
mouse.
What are output devices?
·
Output devices allow you to
output information from the computer and include the printer and the monitor.
The Keyboard
·
An Input device. The keyboard
allows you to type information into the computer. It has evolved over the years
and many people now use a Microsoft style keyboard, which has additional keys
designed to make Microsoft Windows easier to use.
The Mouse
·
An Input device. When using an
operating system, such as Microsoft Windows, you use the mouse to select drop
down menus, to point and click on items, to select items and to drag and drop
items from one place to another.
CD-ROM
·
Most computers are now supplied
with a CD-ROM (Compact Disc - Read Only Memory) drive. CD-ROM discs look
exactly like music CDs but contain computer data instead of music. The
advantage of a CD-ROM is that it can hold a vast amount of data (equivalent to
the storage capacity of over 450 floppy disks). The other big advantage of
CD-ROMs is that they are interchangeable. This means that you can own a range
of different CD-ROMs and choose which one to insert into your CD-ROM drive.
DVD Drives
·
Short for "Digital
Versatile Disc”. Similar to CD-ROM drives but allows you to use DVD disks,
which contain vastly more information than a traditional CD-ROM disk. These
also transfer the data from the disk to the computer far faster, allowing you
to watch movies on your computer screen. A CD-ROM can store 650 MB of data,
while a single-layer, single-sided DVD can store 4.7 GB of data. The two-layer
DVD standard allows a capacity of 8.5 GB. A double-sided DVD increases the
storage capacity to 17 GB (or over 25 times the data storage capacity of a
CD-ROM).
Floppy disk
·
Floppy disks are also known as
diskettes. They are very slow compared to hard disks or CD-ROMs, and hold
relatively small amounts of data (1.44 Mbytes). Sometimes people will backup
(i.e. copy) important data from their hard disk to floppy disks. However, as
diskettes are notoriously unreliable this is not the best way of backing up
valuable data (but is better than nothing).
Zip Disc
·
A Zip disc is like a more
recent version of the floppy disk, the main difference being that a single Zip
disc can hold up to 250 Mbytes of data. They also offer increased speed
compared to the old floppy disk.
Remark! The floppy and Zip disks are now
obsolete. They have been replaced with USB based flash disks. See below.
Hard (Fixed) Disk
·
Hard disks are the main, large
data storage area within your computer. Hard disks are used to store your
operating system, your application programs (i.e. your word processor, games
etc) and your data. They are much faster than CD-ROMs and floppy disks and can
also hold much more data.
USB Flash Disk
·
A USB flash drive consists of a
flash memory data
storage device integrated with a USB (universal serial bus)
interface. USB flash drives are typically removable and rewritable, much
smaller than a floppy disk (1 to 4 inches or 2.5 to
10 cm), and weigh less than 2 ounces (56 g). Storage capacities typically range
from 64 MB to 64 GB with steady improvements in size and price per gigabyte. Some allow 1 million
write or erase cycles and have 10-year data retention, connected by USB 1.1 or USB 2.0.
·
USB flash drives offer
potential advantages over other portable storage devices, particularly the floppy disk. They have a more compact
shape, operate faster, hold much more data, have a more durable design, and
operate more reliably due to their lack of moving parts. Additionally, it has
become increasingly common for computers to ship without floppy disk drives.
USB ports, on the other hand, appear on almost every current mainstream PC and laptop.
These types of drives use the USB
mass storage standard, supported
natively by modern operating systems such as Windows, Mac OS X, Linux, and other Unix-like systems. USB drives with
USB 2.0 support can also operate faster than an optical
disc drive, while storing a larger
amount of data in a much smaller space.
A 16 GB USB flash drive.
The Monitor
·
An Output device. The monitor
is the TV type screen that you view your programs on. They are supplied in
different sizes, common sizes range from 15" to 21" screens. You
should be aware that poor quality or badly maintained monitors could harm your
eyesight.
Additional items or cards
·
Many 'extra' components can
easily be fitted to your computer, which has the advantage of making the
computer 'upgradeable' as newer and better hardware comes along.
Sound cards and speakers
·
Many computers are now supplied
with sound cards and speakers that mean that when you run 'multi-media'
programs, you can listen to sounds that are played back via your computer. If
you have a microphone and suitable software, you can also record sounds. You
can even purchase special software that will allow you to talk to your computer
and get the computer to type the words you have spoken on your screen. In time,
this type of software may replace the keyboard.
Modems
·
A modem is a device that is
used to attach your computer to the telephone system. The modem converts data
into sound that is sent over the telephone line, the receiving modem turns the
sounds back into data. If you wish to connect to the Internet, you will need a
modem.
Printers
·
Most data is printed once you
have created it and there are a vast number of different printers available to
accomplish this. Most common are ink jet and laser printers both of which can
now produce coloured output (at a cost).
Scanners
·
Scanners allow you to scan
printed materials into your computer, which can then be stored within the
computer. These pictures can then be altered, resized and printed as required.
Recordable CDs
·
CD-ROMs are read-only devices,
but increasingly people are purchasing a special type of CD drive unit that
allows you to record data, music or video to your own CDs. These devices
require the purchase of special CDs that you can write to, called CD-R (Compact
Disc – Recordable).
Know how computer memory is measured;
·
Basic Units of Data Storage: It is important to realize that the term digital computer refers
to the fact that ultimately the computer works in what is called binary. Humans
work in tens (because we have 10 fingers). To use the jargon humans work in
base 10. A digital computer uses the numbers 0 and 1 (or on and off if you
prefer). When we talk about computer storage, either the amount of memory (RAM)
or the hard disk capacity we are talking about numbers that are multiples of 0
or 1
·
Bit: All
computers work on a binary numbering system, i.e. they process data in ones or
zeros. This 1 or 0 level of storage is called a bit. Often hardware is specified
as a 32-bit computer, which means that the hardware can process 32 bits at a
time. Software is also described as 16 bit, 32 bit or 64 bit software.
·
Nibble: A nibble consists of 4 Bits
·
Byte: A byte
consists of eight bits i.e 23 = 2 Nibbles = 1 Character
·
Kilobyte: A kilobyte (KB)
consists of 1024 bytes.
·
Megabyte: A megabyte (MB)
consists of 1024 kilobytes, approximately 1,000,000
bytes.
·
Gigabyte: A
gigabyte (GB) consists of 1024 megabytes, approximately 1,000,000,000 bytes.
·
Terabyte: A terabyte (TB) consists
of approximately 1,000,000,000,000 bytes.
·
Files: Data and
programs are stored on your disk as files. There are different types of files,
such as the files that you store your data in, the files that contain your
programs and also files used to store your operating system (such as Microsoft
Windows).
CHARACTERISTICS
OF COMPUTERS
Computers
have certain definite characteristics that make them unique. These
characteristics include:
(a)
Speed: The computers have the ability to execute or
carry out instructions at very great speed.
(b)
Accuracy: Computers per se do not make errors i.e.
there is accuracy of work. Any error is usually caused by the human elements.
(c)
Storage: Computers can store large volume of
data/information on secondary storage, which can be retrieved at a latter time.
(d)
Consistency: Computers have the ability to consistently
follow instructions without getting tired.
(e)
Repetitiveness: Computers have the ability to continue
processing over an extended period.
(f)
Complexity: Computers have the ability to carry out
very complex operations that beats the best human ability.
The Five
Generations of Computers
Each generation of computer is
characterized by a major technological development that fundamentally changed
the way computers operate, resulting in increasingly smaller, cheaper,
more powerful and more efficient and reliable devices.
Read about each generation and the developments that led to the current devices
that we use today.
First Generation - 1940-1956: Vacuum Tubes
The first computers used vacuum tubes for circuitry and magnetic drums for memory.
Their characteristics are:
Ø Very big, taking up entire rooms
Ø Very expensive to operate
Ø Using a great deal of electricity
Ø Generated a lot of heat
Ø Often malfunctions
Ø Relied on machine language to
perform operations
Ø Able to solve only one problem at a time.
Their input was based on punched cards and paper tape. The Output
was displayed on printouts. The UNIVAC and ENIAC
computers are examples of first-generation computing devices.
Second Generation - 1956-1963: Transistors
Transistors replaced
vacuum tubes and ushered in the second generation of computers. Their
characteristics are:
Ø The computers become smaller
Ø They are faster, cheaper and are more energy-efficient
Ø They are more reliable than the first-generation computers.
Ø They used assembly language to
perform operations
Ø Generated lesser heat
Ø Second-generation computers still relied on punched cards for input
and printouts for output.
These were the first computers that stored their instructions in
their memory, which moved from a magnetic drum to magnetic core technology.
The first computers of this generation were developed for the atomic
energy industry.
Third Generation - 1964-1971: Integrated Circuits
The development of the integrated
circuit was the hallmark of the third generation of computers.
Transistors were miniaturized and placed on silicon
chips, called semiconductors.
Characteristics of computers in this generation are:
Ø They were smaller and cheaper than their predecessors.
Ø Drastical increase in speed
Ø The computers are highly efficient
Ø Keyboard is used as input device
Ø Monitor and printouts are used for output
Users interacted with the third generation computers through an operating system, which allowed the device to run
many different applications at one time with
a central program that monitored the memory. Computers for the first time
became accessible to a mass audience because.
Fourth Generation - 1971-Present: Microprocessors
The microprocessor brought the
fourth generation of computers, as thousands of integrated circuits were built
onto a single silicon chip.
Ø What in the first generation filled an entire room could now fit in
the palm of the hand. The Intel 4004 chip, developed in 1971, located all the
components of the computer - from the central
processing unit and memory to input/output controls - on a single chip.
Ø In 1981 IBM introduced its first computer for the home user, and in
1984 Apple introduced the Macintosh. Microprocessors also moved out of the
realm of desktop computers and into many areas of life as more and more
everyday products began to use microprocessors.
Ø As these small computers became more powerful, they could be linked
together to form networks, which eventually led to the development of the
Internet. Fourth generation computers also saw the development of GUIs, the mouse
and handheld devices.
Fifth Generation -
Present and Beyond: Artificial Intelligence
Fifth generation computing devices are based on artificial intelligence. They are still in development. Applications that have been developed so far in this generation are:
Ø Voice
recognition that is being used today.
Ø Parallel processing
and superconductors which is helping to make artificial intelligence a reality.
Ø Quantum computation,
molecular and nanotechnology
will radically change the face of computers in years to come.
The goal of fifth-generation computing is
to develop devices that respond to natural language
input and are capable of learning and self-organization.
|
The first computers were people! That is, electronic computers (and
the earlier mechanical computers) were given this name because they performed
the work that had previously been assigned to people. "Computer" was
originally a job title: it was used to describe those human beings
(predominantly women) whose job was to perform the repetitive calculations
required to compute such things as navigational tables, tide charts, and
planetary positions for astronomical almanacs. Imagine you had a job where hour
after hour, day after day, you were to do nothing but compute multiplications.
Boredom would quickly set in, leading to carelessness, leading to mistakes. And
even on your best days you wouldn't be producing answers very fast. Therefore,
inventors have been searching for hundreds of years for a way to mechanize
(that is, find a mechanism that can perform) this task.
This picture shows what were known as "counting
tables" [photo courtesy IBM]
A typical computer operation back when computers were
people.
The abacus was an early aid for mathematical
computations. Its only value is that it aids the memory of the human performing
the calculation. A skilled abacus operator can work on addition and subtraction
problems at the speed of a person equipped with a hand calculator
(multiplication and division are slower). The abacus is often wrongly
attributed to China.
In fact, the oldest surviving abacus was used in 300 B.C. by the Babylonians.
The abacus is still in use today, principally in the far east. A modern abacus
consists of rings that slide over rods, but the older one pictured below dates
from the time when pebbles were used for counting (the word
"calculus" comes from the Latin word for pebble).
A very old abacus
A more modern abacus. Note how the abacus is really
just a representation of the human fingers: the 5 lower rings on each rod
represent the 5 fingers and the 2 upper rings represent the 2 hands.
In 1617 an eccentric (some say mad) Scotsman named John Napier
invented logarithms, which are a technology that allows
multiplication to be performed via addition. The magic ingredient is the
logarithm of each operand, which was originally obtained from a printed table.
But Napier also invented an alternative to tables, where the logarithm values
were carved on ivory sticks which are now called Napier's Bones.
An original set of Napier's Bones [photo courtesy IBM]
A more modern set of Napier's Bones
Napier's invention led directly to the slide rule,
first built in England
in 1632 and still in use in the 1960's by the NASA engineers of the Mercury,
Gemini, and Apollo programs which landed men on the moon.
A slide rule
Leonardo da Vinci (1452-1519) made drawings of gear-driven
calculating machines but apparently never built any.
A Leonardo da Vinci drawing showing gears arranged for
computing
The first gear-driven calculating machine to actually be built was
probably the calculating clock, so named by its inventor, the
German professor Wilhelm Schickard in 1623. This device got little publicity
because Schickard died soon afterward in the bubonic plague.
Schickard's Calculating Clock
In 1642 Blaise Pascal, at age 19, invented the Pascaline
as an aid for his father who was a tax collector. Pascal built 50 of this
gear-driven one-function calculator (it could only add) but couldn't sell many
because of their exorbitant cost and because they really weren't that accurate
(at that time it was not possible to fabricate gears with the required
precision). Up until the present age when car dashboards went digital, the
odometer portion of a car's speedometer used the very same mechanism as the
Pascaline to increment the next wheel after each full revolution of the prior
wheel. Pascal was a child prodigy. At the age of 12, he was discovered doing
his version of Euclid's
thirty-second proposition on the kitchen floor. Pascal went on to invent
probability theory, the hydraulic press, and the syringe. Shown below is an 8
digit version of the Pascaline, and two views of a 6 digit version:
Pascal's Pascaline [photo © 2002 IEEE]
A 6 digit model for those who couldn't afford the 8
digit model
A Pascaline opened up so you can observe the gears and
cylinders which rotated to display the numerical result
The Jacquard loom was one of the first
programmable devices.
A succession of steadily more
powerful and flexible computing devices were constructed in the 1930s and
1940s, gradually adding the key features that are seen in modern computers. The
use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible
programmability were vitally important steps, but defining one point along this
road as "the first digital electronic computer" is difficult (Shannon 1940). Notable achievements
include:.jpg "\"EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.\"")
EDSAC
was one of the first computers to implement the stored program (von Neumann)
architecture.
- Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
- The non-programmable Atanasoff–Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.
- The secret British Colossus computers (1943)[8], which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
- The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
- The U.S. Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.
Today, we have computer systems that are
small, fast and highly reliable like the one shown below.
|
Computers can be
classified based on the following parameters:
Ø
Type
of data processed
Ø
The
size
Ø
The
Purpose or scope
Ø
The
age of technology
Classification
by type of data processed
In this category,
we have
v
Digital
computers
v
Analog
computers
v
Hybrid
computers
a. Digital computer
These are computers that operate on discrete values. That is, values that
occur at a point in time. E.g. 0,1,2,3… The output from digital computers is
usually in the form of discrete values. This class of computers is commonly
found in the business environments, and they include Desk Calculators, Adding
machines, and most of the computers we have around, that is, the personal
computers.
b.
Analog computer
An analog
computer is a form of computer that uses continuous physical
phenomena such as electrical, mechanical, or hydraulic quantities to model the
problem being solved. The output of analog computers is usually represented in
the form of smooth curves or graphs from which information can be read.
Electronic
analog computers
Mechanical analog computers
In general, analog computers are limited
by real, non-ideal effects.
These are examples of analog computers
that have been constructed or practically used:
- differential analyzer
- Kerrison Predictor
- mechanical integrator
- MONIAC Computer (hydraulic model of UK economy)
- operational amplifier
- planimeter
- Rangekeeper
- slide rule
- thermostat
- Torpedo Data Computer
- Water integrator
- Mechanical computer
c.
Hybrid computer
Hybrid
computers are computers
that comprise features of analog computers and digital computers.
The digital component normally serves as the controller and provides logical
operations, while the analog component normally serves as a solver of
differential equations.
In general, analog computers are
extraordinarily fast, since they can solve most complex equations at the rate
at which a signal traverses the circuit, which is generally an appreciable
fraction of the speed of light. On the other hand, the precision of analog
computers is not good; they are limited to three, or at most, four digits of
precision.
Hybrid computers can be used to obtain a
very good but relatively imprecise 'seed' value, using an analog computer front-end,
which is then fed into a digital computer iterative process to achieve the
final desired degree of precision. With a three or four digit, highly accurate
numerical seed, the total digital computation time necessary to reach the desired precision is dramatically reduced,
since many fewer iterations are required.
Consider that the nervous
system in animals is a form of hybrid computer. Signals pass across
the synapses
from one nerve cell
to the next as discrete (digital) packets of chemicals, which are then summed
within the nerve cell in an analog fashion by building an electro-chemical
potential until its threshold is reached, whereupon it discharges and sends out a
series of digital packets to the next nerve cell. The advantages are at least
threefold: noise within the system is minimized (and tends not to be additive),
no common grounding system is required, and there is minimal degradation of the
signal even if there are substantial differences in activity of the cells along
a path (only the signal delays tend to vary). The individual nerve cells are
analogous to analog computers; the synapses are analogous to digital computers.
Note that hybrid computers should
be distinguished from hybrid systems. The latter may be no more than a
digital computer equipped with an Analog-to-digital converter at the input
and/or a Digital-to-analog converter at the output,
to convert analog signals for ordinary digital signal processing, and
conversely, e.g., for driving physical control systems, such as
servomechanisms.
Classification
by Purpose or Scope
Using scope as a criterion,
computers can be classified into two broad categories:
(a)
Dedicated or Special purpose computers: These are
computers that are designed to carry out only specified task. The series of
instructions that these types of computer follow to carry out its operation is
in-built and cannot be modified. E.g. word processor, robots used in car
manufacturing plants.
(b)
General Purpose Computers: These are computers designed
to perform a wide variety of operations. They can be programmed to carry out
scientific oriented applications or business oriented ones just by changing the
series of instructions in its memory.
Classification
by Size
Using physical size as a
factor, the following types of computers can be identified:
(a)
Micro-Computers: These are computers that are small in
size which can be placed on the desk or lap or palm.
(b)
Mini Computers: These are large computers that support
multi users. Their speed of operations is high compared to micros.
(c)
Mainframe Computers: These are very large computers
that support multi users. Their speed of operations and memory capacity is
larger than that of a mini computer.
Classification by Age of
Technology
This classification is also referred to as
generations of computers. See our discussion on generations of computers in
week three.
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The most common input devices used by the computer are the keyboard and mouse. The keyboard allows the entry of textual information while the mouse allows the selection of a point on the screen by moving a screen cursor to the point and pressing a mouse button.
Many input devices can be classified according to:
- the modality of input (e.g. mechanical, motion, audio, visual, etc.)
- whether the input is discrete (e.g. key presses) or continuous (e.g. a mouse's position, though digitized into a discrete quantity, is fast enough to be considered continuous)
- the number of degrees of freedom involved (e.g. two-dimensional traditional mice, or three-dimensional navigators designed for CAD applications)
- Whether the input is direct or indirect. With direct input, the input space coincides with the display space, i.e. pointing is done in the space where visual feedback or the cursor appears. Touch screens and light pens involve direct input. Examples involving indirect input include the mouse and trackball.
- Whether the positional information is absolute (e.g. on a touch screen) or relative (e.g. with a mouse that can be lifted and repositioned)
A keyboard is a human interface
device which is represented as a layout of buttons. Each button, or
key, can be used to either input a linguistic character to a computer, or to
call upon a particular function of the computer. Traditional keyboards use
spring-based buttons, though newer variations employ virtual keys, or even projected keyboards.
A pointing device is any human
interface device that allows a user to input spatial data to a computer. In the
case of mice and touch screens, this is usually achieved by detecting movement
across a physical surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting
their angle of deflection. Movements of the pointing device are echoed on the
screen by movements of the cursor,
creating a simple, intuitive way to navigate a computer's GUI.High-degree of freedom input devices
- Wired glove
- Fiber optic sensors (For example, ShapeTape)
- Magnetic or ultrasonic motion tracking devices
- 3D or 6D Mice
- Some haptic devices
Wii Remote with attached strap
Input devices, such as buttons
and joysticks, can be combined on a single physical device that could be
thought of as a composite device. Many gaming devices have controllers like this.
Technically mice are composite devices, as they both track movement and provide
buttons for clicking, but composite devices are generally considered to have
more than two different forms of input.- Game controller
- Gamepad (or joypad)
- Paddle (game controller)
- Wii Remote
In the fashion of video devices, audio devices are used to either capture or create sound. In some cases, an audio output device can be used as an input device, in order to capture produced sound.
- Microphone
- MIDI keyboard or other digital musical instrument
Imaging and Video input devices
- Webcam
- Image scanner
- Fingerprint scanner
- Barcode reader
- 3D scanner
- Laser rangefinder
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An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the system to the outside.
The most common outputs are monitors and speakers.
A visual display unit (also called VDU, monitor, or screen) offers a
two-dimensional visual presentation of information a device that display
information on a screen.
b. Speaker
A speaker can be used for various sounds meant to alert the user, as well
as music and spoken text.
Printers produce a permanent hard copy of the information on paper. A
computer peripheral that place texts on paper.
- Computer display, display device
- Computer printer
- Film recorder
- Industrial Digital Printers
- Plotter
- Head-mounted display
- Projectors
- Volumetric displays
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Computer data storage, often called storage or memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s.
In contemporary usage, memory usually refers to a form of semiconductor storage known as random access memory (RAM) and sometimes other forms of fast but temporary storage. Similarly, storage today more commonly refers to mass storage - optical discs, forms of magnetic storage like hard disks, and other types slower than RAM, but of a more permanent nature. Historically, memory and storage were respectively called primary storage and secondary storage.
The contemporary distinctions are helpful, because they are also fundamental to the architecture of computers in general. As well, they reflect an important and significant technical difference between memory and mass storage devices, which has been blurred by the historical usage of the term storage. Nevertheless, this article uses the traditional nomenclature.
Primary storage
Primary storage, presently known as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them. Any data actively operated on is also stored there in uniform manner.Historically, early computers used delay lines, Williams tubes, or rotating magnetic drums as primary storage. By 1954, those unreliable methods were mostly replaced by magnetic core memory, which was still rather cumbersome. Undoubtedly, a revolution was started with the invention of a transistor, that soon enabled then-unbelievable miniaturization of electronic memory via solid-state silicon chip technology.
This led to a modern random access memory (RAM). It is small-sized, light, but quite expensive at the same time. (The particular types of RAM used for primary storage are also volatile, i.e. they lose the information when not powered).
As shown in the diagram, traditionally there are two more sub-layers of the primary storage, besides main large-capacity RAM:
- Processor registers are located inside the processor. Each register typically holds a word of data (often 32 or 64 bits). CPU instructions instruct the arithmetic and logic unit to perform various calculations or other operations on this data (or with the help of it). Registers are technically among the fastest of all forms of computer data storage.
- Processor cache is an intermediate stage between ultra-fast registers and much slower main memory. It's introduced solely to increase performance of the computer. Most actively used information in the main memory is just duplicated in the cache memory, which is faster, but of much lesser capacity. On the other hand it is much slower, but much larger than processor registers. Multi-level hierarchical cache setup is also commonly used—primary cache being smallest, fastest and located inside the processor; secondary cache being somewhat larger and slower.
As the RAM types used for primary storage are volatile (cleared at start up), a computer containing only such storage would not have a source to read instructions from, in order to start the computer. Hence, non-volatile primary storage containing a small startup program (BIOS) is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access).
Many types of "ROM" are not literally read only, as updates are possible; however it is slow and memory must be erased in large portions before it can be re-written. Some embedded systems run programs directly from ROM (or similar), because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, rather use large capacities of secondary storage, which is non-volatile as well, and not as costly.
When accessing memory, a fast processor will demand a great deal from RAM. At worst, the CPU may have to waste clock cycles while it waits for data to be retrieved. Faster memory designs and motherboard buses can help, but since the 1990s "cache memory" has been employed as standard between the main memory and the processor. Not only this, CPU architecture has also evolved to include ever larger internal caches. The organisation of data this way is immensely complex, and the system uses ingenious electronic controls to ensure that the data the processor needs next is already in cache, physically closer to the processor and ready for fast retrieval and manipulation.
1 GiB of SDRAM
mounted in a personal computer.
An example of primary storage.
Secondary
storage
Secondary storage, or storage in popular usage,
differs from primary storage in that it is not directly accessible by the CPU.
The computer usually uses its input/output channels to access secondary
storage and transfers the desired data using intermediate
area in primary storage. Secondary storage does not lose the data
when the device is powered down—it is non-volatile. Per unit, it is typically
also an order of magnitude less expensive than primary storage. Consequently,
modern computer systems typically have an order of magnitude more secondary
storage than primary storage and data is kept for a longer time there.In modern computers, hard disks are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored in random access memory is measured in billionths of a second, or nanoseconds. This illustrates the very significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times.
Some other examples of secondary storage technologies are: flash memory (e.g. USB sticks or keys), floppy disks, magnetic tape, paper tape, punch cards, standalone RAM disks, and Zip drives. Note that floppy disk, paper tape, punch cards and Zip drives are now obsolete.
The secondary storage is often formatted according to a filesystem format, which provides the abstraction necessary to organize data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information.
Most computer operating systems use the concept of virtual memory, allowing utilization of more primary storage capacity than is physically available in the system. As the primary memory fills up, the system moves the least-used chunks (pages) to secondary storage devices (to a swap file or page file), retrieving them later when they are needed. As more of these retrievals from slower secondary storage are necessary, the more the overall system performance is degraded.
40 GB hard disk drive (HDD); when connected to
a computer it serves as secondary storage.
160 GB SDLT tape
cartridge, an example of off-line storage. When used within a robotic tape library, it is classified as tertiary
storage instead.
Many different forms of storage,
based on various natural phenomena, have been invented. So far, no practical
universal storage medium exists, and all forms of storage have some drawbacks.
Therefore a computer system usually contains several kinds of storage, each
with an individual purpose.A digital computer represents data using the binary numeral system. Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0. The most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, using eight million bits, or about one megabyte, a typical computer could store a small novel.
Traditionally the most important part of every computer is the central processing unit (CPU, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components.
Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators or simple digital signal processors. Von Neumann machines differ in that they have a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that a relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines.
In practice, almost all computers use a variety of memory types, organized in a storage hierarchy around the CPU, as a tradeoff between performance and cost. Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit.
Various forms of
storage, divided according to their distance from the central processing
unit. The fundamental components of a general-purpose computer are arithmetic and
logic unit, control circuitry,
storage space, and input/output
devices. Technology and capacity as in common home computers around 2005.
Recently,
primary storage and secondary storage in some uses refer to what
was historically called, respectively, secondary storage and tertiary
storage.[1]Secondary storage
A hard disk drive
with protective cover removed.
Tertiary storage
Large tape library. Tape cartridges placed on
shelves in the front, robotic arm moving in the back. Visible height of the
library is about 180 cm.
Tertiary
storage or tertiary
memory, provides a third level of storage. Typically it involves a robotic
mechanism which will mount (insert) and dismount removable mass
storage media into a storage device according to the system's demands; this
data is often copied to secondary storage before use. It is primarily used for
archival of rarely accessed information since it is much slower than secondary
storage (e.g. 5-60 seconds vs. 1-10 milliseconds). This is primarily useful for
extraordinarily large data stores, accessed without human operators. Typical
examples include tape libraries
and optical jukeboxes.
When a computer needs to read
information from the tertiary storage, it will first consult a catalog database to determine which tape or disc
contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place
it in a drive. When the computer has finished reading the information, the
robotic arm will return the medium to its place in the library.Off-line storage
Off-line storage, also known as disconnected storage, is a computer data storage on a medium or a device that is not under the control of a processing unit. The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.Off-line storage is used to transfer information, since the detached medium can be easily physically transported. Additionally in case a disaster, for example a fire, destroys the original data, a medium in a remote location will be probably unaffected, enabling disaster recovery. Off-line storage increases a general information security, since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is accessed seldom or never, off-line storage is less expensive than tertiary storage.
In modern personal computers, most secondary and tertiary storage media are also used for off-line storage. Optical discs and flash memory devices are most popular, and to much lesser extent removable hard disk drives. In enterprise uses, magnetic tape is predominant. Older examples are floppy disks, Zip disks, or punched cards.
A 1GB DDR RAM
memory module
Storage technologies at all
levels of the storage hierarchy can be differentiated by evaluating certain
core characteristics as well as measuring characteristics specific to a
particular implementation. These core characteristics are volatility,
mutability, accessibility, and addressibility. For any particular
implementation of any storage technology, the characteristics worth measuring
are capacity and performance.Volatility
Will retain the
stored information even if it is not constantly supplied with electric power.
It is suitable for long-term storage of information. Nowadays used for most of
secondary, tertiary, and off-line storage. In 1950s and 1960s, it was also used
for primary storage, in the form of magnetic core
memory.
Requires constant
power to maintain the stored information. The fastest memory technologies of
today are volatile ones (not a universal rule). Since primary storage is
required to be very fast, it predominantly uses volatile memory.
Differentiation
A form of
volatile memory which also requires the stored information to be periodically
re-read and re-written, or refreshed,
otherwise it would vanish.
A form of volatile
memory similar to DRAM with the exception that it does not refresh on occasion.
Mutability
Read/write
storage or mutable storage
Allows
information to be overwritten at any time. A computer without some amount of
read/write storage for primary storage purposes would be useless for many
tasks. Modern computers typically use read/write storage also for secondary
storage.
Read only
storage
Retains the
information stored at the time of manufacture, and write once storage (WORM)
allows the information to be written only once at some point after manufacture.
These are called immutable storage. Immutable storage is used for
tertiary and off-line storage. Examples include CD-ROM and CD-R.
Slow write, fast read storage
Read/write
storage which allows information to be overwritten multiple times, but with the
write operation being much slower than the read operation. Examples include CD-RW.
Accessibility
Any location in
storage can be accessed at any moment in approximately the same amount of time.
Such characteristic is well suited for primary and secondary storage.
The accessing of
pieces of information will be in a serial order, one after the other; therefore
the time to access a particular piece of information depends upon which piece
of information was last accessed. Such characteristic is typical of off-line
storage.
How Computers WorkA general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.
Figure 8.1: Inside the computer
Control unit
The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer. Control systems in advanced computers may change the order of some instructions so as to improve performance.A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:
- Read the code for the next instruction from the cell indicated by the program counter.
- Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
- Increment the program counter so it points to the next instruction.
- Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
- Provide the necessary data to an ALU or register.
- If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
- Write the result from the ALU back to a memory location or to a register or perhaps an output device.
- Jump back to step (1).
It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program - and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.
Arithmetic/logic unit (ALU)
The ALU is capable of performing two classes of operations: arithmetic and logic.The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.
Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.
Memory
Magnetic core
memory was popular main memory for computers through the 1960s until
it was completely replaced by semiconductor memory.
A computer's memory can be viewed
as a list of cells into which numbers can be placed or read. Each cell has a
numbered "address" and can store a single number. The computer can be
instructed to "put the number 123 into the cell numbered 1357" or to
"add the number that is in cell 1357 to the number that is in cell 2468
and put the answer into cell 1595". The information stored in memory may
represent practically anything. Letters, numbers, even computer instructions
can be placed into memory with equal ease. Since the CPU does not differentiate
between different types of information, it is up to the software to give
significance to what the memory sees as nothing but a series of numbers.In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells
called registers
that can be read and written to much more rapidly than the main memory area.
There are typically between two and one hundred registers depending on the type
of CPU. Registers are used for the most frequently needed data items to avoid
having to access main memory every time data is needed. Since data is
constantly being worked on, reducing the need to access main memory (which is
often slow compared to the ALU and control units) greatly increases the
computer's speed.Figure 8.2: The Central Processing Unit (CPU)
Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM as discussed earlier. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.
ow the CPU Executes Program Instructions
Let us examine the way the central processing unit, in association with memory, executes a computer program. We will be looking at how just one instruction in the program is executed. In fact, most computers today can execute only one instruction at a time, though they execute it very quickly. Many personal computers can execute instructions in less than one-millionth of a second, whereas those speed demons known as supercomputers can execute instructions in less than one-billionth of a second.
Let us examine the way the central processing unit, in association with memory, executes a computer program. We will be looking at how just one instruction in the program is executed. In fact, most computers today can execute only one instruction at a time, though they execute it very quickly. Many personal computers can execute instructions in less than one-millionth of a second, whereas those speed demons known as supercomputers can execute instructions in less than one-billionth of a second.
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Figure 8.3: The Machine Cycle
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- Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage device (the process is further complicated by the fact that, as we noted earlier, the data will probably make a temporary stop in a register). As Figure 8.3 shows, once the necessary data and instruction are in memory, the central processing unit performs the following four steps for each instruction:
- The control unit fetches (gets) the instruction from memory.
- The control unit decodes the instruction (decides what it means) and directs that the necessary data be moved from memory to the arithmetic/logic unit. These first two steps together are called instruction time, or I-time.
- The arithmetic/logic unit executes the arithmetic or logical instruction. That is, the ALU is given control and performs the actual operation on the data.
- Thc arithmetic/logic unit stores the result of this operation in memory or in a register. Steps 3 and 4 together are called execution time, or E-time.
The control unit eventually directs memory to release the result to an output device or a secondary storage device. The combination of I-time and E-time is called the machine cycle. Figure 8.4 shows an instruction going through the machine cycle.
Each central processing unit has an internal
clock that produces pulses at a fixed rate to synchronize all computer
operations. A single machine-cycle instruction may be made up of a substantial
number of sub-instructions, each of which must take at least one clock cycle.
Each type of central processing unit is designed to understand a specific group
of instructions called the instruction set. Just as there are many different
languages that people understand, so each different type of CPU has an
instruction set it understands. Therefore, one CPU-such as the one for a Compaq
personal computer-cannot understand the instruction set from another CPU-say,
for a Macintosh.
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Figure 8.4: The Machine Cycle in Action
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Figure 8.5:
Memory Addresses Like Mailboxes
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It is one thing to have instructions and data somewhere
in memory and quite another for the control unit to be able to find them. How
does it do this?
The location in memory for each
instruction and each piece of data is identified by an address. That is, each
location has an address number, like the mailboxes in front of an apartment
house. And, like the mailboxes, the address numbers of the locations remain the
same, but the contents (instructions and data) of the locations may change.
That is, new instructions or new data may be placed in the locations when the
old contents no longer need to be stored in memory. Unlike a mailbox, however,
a memory location can hold only a fixed amount of data; an address can hold only
a fixed number of bytes - often two bytes in a modern computer.
Figure 8.5 shows how a program manipulates data in memory. A payroll program, for example, may give instructions to put the rate of pay in location 3 and the number of hours worked in location 6. To compute the employee's salary, then, instructions tell the computer to multiply the data in location 3 by the data in location 6 and move the result to location 8. The choice of locations is arbitrary - any locations that are not already spoken for can be used. Programmers using programming languages, however, do not have to worry about the actual address numbers, because each data address is referred to by a name. The name is called a symbolic address. In this example, the symbolic address names are Rate, Hours, and Salary.
Figure 8.5 shows how a program manipulates data in memory. A payroll program, for example, may give instructions to put the rate of pay in location 3 and the number of hours worked in location 6. To compute the employee's salary, then, instructions tell the computer to multiply the data in location 3 by the data in location 6 and move the result to location 8. The choice of locations is arbitrary - any locations that are not already spoken for can be used. Programmers using programming languages, however, do not have to worry about the actual address numbers, because each data address is referred to by a name. The name is called a symbolic address. In this example, the symbolic address names are Rate, Hours, and Salary.
COMPUTER
SOFTWARE
Computer
software is basically a program, which allows the hardware components to
operate effectively as well as provide very many useful services. Computer
manufacturers and certain software specialist usually write software. Programs
are sequences of instructions given to a computer to enable it solve a
particular problem or accomplish a given assignment.
Some of these
programs are permanently stored in the computer. They automatically start up the
computer when it is switched on. On completion of the initial process of
start-up, they will transfer control to the operating system, which is the
manager of the computer resources. The rest of these programs that are for the
external use are loaded to the memory of the system from the secondary storage
medium like hard/floppy disk after the system boot-up. The loading of the
operating system is automatic, hence if It is not loaded, the system cannot
boot or prompt for a command.
Categories of Software
The tree diagram
below illustrates the different categories of software and, to some extent,
their relationships to each other. This section examines the distinction
between systems software and applications software.
Categories of software
System Software
The term systems
software covers the collection of programs usually supplied by the manufacturer
of the computer. These programs protect the user from the enormous complexity
of the computer system, and enable the computer to be used to maximum effect by
a wide variety of people, many of whom will know very little about the inner
workings of computers. Without systems software a modern digital computer would
be virtually impossible to use
Broadly
speaking, systems software consists of three elements:
-
those programs concerned with
the internal control and co-ordination of all aspects of the computer system,
namely the operating system;
-
a number of other programs
providing various services to users. These services include translators for
any languages supported by the system and utility programs such as pro
gram editors and other aids to programming;
-
graphical user interfaces (GUls) providing intuitive, easily learned methods for using
microcomputer systems.
Operating systems
If a computer
system is viewed as a set of resources, comprising elements of both hardware
and software, then it is the job of the collection of programs known as the
operating system to manage these resources as efficiently as possible. In so doing,
the operating system acts as a buffer between the user and the complexities of
the computer itself. One way of regarding the operating system is to think of
it as a program which allows the user to deal with a simplified computer, but
without losing any of the computational power of the machine. In this way the
computer system becomes a virtual system, its enormous complexity hidden and
controlled by the operating system and through which the user communicates with
the real system.
The main functions of operating systems
Earlier it was
stated that the function of an operating system is to manage the resources of
the computer system. Generally these resources managed by Operating System are
CPU, Memory, Input/Output Devices, Backing Store and Files.
The above is by
no means a full list of the functions of an operating system. Other functions
include:
-
interpretation of the command
language by which operators can communicate with the operating system;
-
error handling. For example,
detecting and reporting inoperative or malfunctioning peripherals;
-
protection of data files and
programs from corruption by other users;
-
Security: protection of data
files and programs from unauthorized use;
-
Accounting: accounting and
logging of the use of the computer resources.
-
Program Loading to the main
memory for processing
-
Multiprogramming
-
Interrupt handling
-
Job Sequencing
-
File Management
-
Job Scheduling
-
Peripheral Control
-
Recovery from System Failure
Some current
operating systems are OS/2, Windows 95, 98, ME, UNIX, MS-DOS, Windows NT etc.
Types of Operating System
-
Single Program OS: allow one user’s program at a time
-
Simple Batch Systems: Provides multiprogramming of batch programs but have few facilities
for multi-access
-
Multi-access and
Time-sharing: Allows multiple access to system
resources and therefore share processors time to cope with numerous users
-
Real-time system: Used in any real time data processing technique
System Services
Often a manufacturer will provide a
number of programs designed specifically for program or application
development. Some examples of such aids
are as follows.
Language Translators (Processors)
These are
computer programs designed to convert high-level language programs into machine
code, that is, into a form directly usable by a computer. Common types of
language processors are Assembler, Compilers and Interpreters.
Assembler: This is a translator that convert program written in Assembly
language to machine code and vice-versa.
Compiler: This is a translator that convert program written in High Level
Language to machine code and vice-versa, and the translation in done all at
once. Languages translated by Compiler are COBOL, FORTRAN, C++ etc.
Interpreter: This is a translator that convert program written in High Level
language to machine code and vice-versa, but the translator is done line by
line. Example of language translated by Interpreter is BASIC.
Utility
Programs
As part of the
systems software provided with a computer system there are a number of utility
programs specifically designed to aid program development and testing. These
include the following.
Editors: These permit the creation and modification of source programs and data files.
Debugging Aids : Debugging aids help
programmers to isolate and identify the cause of bugs.
File managers: These simplify and facilitate a number of operations connected with program development and maintenance such as keeping backup copies of important files; deleting, creating, merging, sorting files etc.
Without the help of such dedicated
programs, operations such as these could be extremely time-consuming and
consequently expensive.
Graphical
User Interfaces (GUls)
The vast
majority of microcomputer users are interested merely in using a computer as a
tool, without any real interest in the technical details of its operation. A
typical user will probably want to run one or more common general-purpose
applications, organize files into directories, delete files and format disks.
Though the operating system will provide these services, the user needs to have
a certain amount of technical knowledge to perform these tasks, Graphical
user interfaces (or GUI, pronounced Gooey) provide a more intuitive
means of performing common tasks. They usually make use of a pointing device,
typically a mouse, by means of which a pointer is moved around
the monitor screen on which small pictures (or icons) are displayed.
These icons represent, among other things, programs which can be run by moving
the mouse pointer over the icon and then clicking one of the buttons on the
mouse. Applications run in their own self-contained areas called windows. In
addition, it is usually possible to activate pull-down menus which
provide access to standard functions. When a GUI uses Windows, Icons, Mouse,
Pointers and Pull-down menus, it is referred to as a WIMP environment.
USER APPLICATIONS SOFTWARE
Applications
software refers to programs that have some direct value to an organisation, and
will normally include those programs for which the computer system was specifically
purchased. Application Software are grouped into User Program and Commercially
produced applications software.
User Programs: are written by people within the organization for specific needs,
which cannot be satisfied by other sources of software. These program writers
may be professional programmers employed by the organization, or other casual
users with programming expertise.
Commercial Packages
These are the
kind of application packages that are produced by software professionals and be
sold for a wide variety of users. This falls into two main categories:
a)
Special-purpose packages: Though commercial, it is designed for a
specific purpose like a department or a section of an organization. Examples
are
- Airline Seat Reservation,
- Theatre Seat Reservation
- Hotel Room Reservation .
- Point of Sales Software
- A Payroll Program
Program
for each of these areas are of use only in their specific area of application
and their use will be confined to a specific department of the business. A Payroll
Program for example, can only be used for Payroll and will be used by Payroll
staff only.
b) General
Purpose:
These provide facilities which might be used in a wide variety of business
situation and which might therefore be used across many department of business
e.g.
1. Word-processing: These programs
that, more or less, turn a computer system into a powerful typewriting tool and
more. It helps us to produce letters, reports, magazines, memos, etc. Example
of Word-processing programs are: .WordStar, WordPerfect, PC Write, MultiMate,
Ten Best and WordStar 2000.
2. Database Management: They store and
retrieve information such as customer lists, inventories and notes. These
programs help us to record and maintain information about people, places, things
and management reports of all types. Examples are Dbase III & IV, FoxBASE,
Oracle, FoxPro and Clipper, MICROSOFT ACCESS, Paradox,
3. Spreadsheet: Spreadsheets are
software packages that, more or less,
turn a computer system into a sophisticated electronic calculator. Many
Spreadsheet packages also have presentation graphics generators, which take
data and painlessly convert them into bar charts, line charts, and the like.
These programs help us to produce financial reports and other mathematical computations.
Examples are Lotus 1-2-3,
QuatoPro, SuperCalc, Multiplan, VP Planner, Planning Assistant and Microsoft
Excel.
5. Desktop Publishing & Graphics Programs:
Graphics programs create graphs and drawings that can be used in newsletters,
posters, advertisements and other documents. Some allow users to import
photographs into documents or create animated pictures for use in
"multimedia" presentations. Popular graphics programs include PC
Paintbrush, Illustrator, Persuasion, Cricket Draw, Corel Draw, Print Master,
Print Shop, Microsoft PowerPoint, and Harvard Graphics.
7. Communication Software: This allows
communications and networking. Examples are Internet Explorer, Netscape
Navigator
ADVANTAGES
OF CUSTOM APPLICATION SOFTWARE (USER PROGRAMS)
1.
The needs of the organization are precisely met
2.
The method of inputting/outputting data may be designed to suit user’s taste.
3.
It may require less memory and less disk space.
4.
Program may execute faster
5.
Programs can be changed to meet changing conditions.
DISADVANTAGES
1.
Development time may be lengthy
2.
Human resources needed for development may not be available
3.
High cost of development (since it is designed for only one organization).
4.
Cost of maintenance / upgrading may be high.
ADVANTAGES
OF GENERIC APPLICATION SOFTWARE (COMMERCIAL APPLICATION PACKAGES)
1.
Availability is immediate as only installation process is necessary before it
can start being productive.
2.
Cost is less as it is spread among a number of users who purchase the product.
3.
Reliability may be greater as it is thoroughly tested before it is marketed.
DISADVANTAGES
1.
It may not be an exact match for needs
2.
It may require more system resources. Programs are frequently longer, thereby,
requiring more memory and disk space
3.
It is not adapted to changing needs
4.
It may execute more slowly.
GUIDELINE FOR
ACQUISITION OF APPLICATION SOFTWARE
1.
The software to be acquired must be one whose use will improve the particular
operating function of that business.
2.
It must be of high performance
3.
The software to be acquired must be one with enough ease in learning.
4.
The software to be acquired must be available when needed
5.
If a software package is complex then training is required
6.
Good documentation: The package to be used must be properly documented. This
should include how the package is to be installed how to use the package and
other necessary technical details.
7.
Users friendliness: The package must be easy to use even by non- computer
specialists.
8.
Compatibility of the package: Before a package program can be adopted, it must
be compatible with the user system requirements as well as with the user’s
hardware.
SOCIAL IMPLICATION OF COMPUTERS ON THE
SOCIETY
Given below are some of the areas the gains
of information technology (computer age) have manifested:
(a) The Office
(b) Manufacturing Industry
(c) Health
(d) Finance and Commerce
(e) Military Institution
(f) Education and Training
(g) Leisure
THE OFFICE:
The Mechanised Office
started in the second half of the 19th Century with the introduction
of Typewriter and Telegraph. Within the 1st half of the
20th Century, additional office technologies had been developed.
These are: Automatically switched Telephone, Electric Typewriter, Telex,
Duplicating machines, Adding Machines, etc. The rise of Electronics during and
after the Second World War brought about a gradual replacement of the
Mechanical equipment by the smaller, more reliable more versatile equivalent,
e.g. Private Branch Telephone Exchange, Electronic Typewriters, Display
Terminals, Copiers and Computers.
Office
Automation helps to keeps management about the state of production, stocks, and
personnel etc, as part of management information system (MIS).
More interestingly
today, is the talk about electronic office. This is where an office will have a
central computer connected to by various officers via terminals in their homes
and carry out their official assignments. The most important advantage of this
system is speed at which jobs are handled with this system and cutting of cost
of transportation by staff from their homes to their various offices. The
demerit lies in the fact that their would be lack of social interaction among
staff and inadequate privacy of data and job operations. As well there would be
lack of superior control of subordinates and the cost of implementing such a
system is high.
MANUFACTURING INDUSTRY:
Manufacturing
Industries are among the first and most well established fields of application
of information technology. It has provided tools for production planning,
production design and industrial research. The earliest application of
information technology to the manufacturing industries was the Jacquard Loom,
where the weaving pattern was controlled by sequence of punched cards. Based on
principle, the Numerical Control (NC) of Machine tools came to being in 1952
and started to appear commercially in the early 60’s and took another 10 years
before the Paper Tape was replaced by programs stored in the memory of the
computers. In such Computer Numerical control (CNC) Machine, various aspects of
the machine processing happen under a pre-programmed computer control.
Other areas
where information technology has done very well are Computer integrated manufacturing
(CIM), Computer Aided Manufacturing (CAM), computer Aided Design (CAD).
Computer Aided Design was successfully applied to many fields outside the
manufacturing unit, such as computer itself, Architectural and Building
Industries.
HEALTH:
Computer-Controlled
life support systems can monitor a patient’s condition via a number of sensor
devices checking on, for example, pulse rate, body temperature and blood
pressure. This frees nurses for other duties. Computed-assisted diagnosis
systems make use of artificial intelligence to assist a physician in diagnosing
a patient condition. Another interesting development is the use of the computer
to assist the plastic surgeon in the repairs of facial injuries or deformities.
FINANCE AND COMMERCE:
Every money
transactions are of importance to information technology. A record usually
needs to be made either formally or informally about the amount, the purpose,
the parties involved, and the date of transaction etc previously recorded on
paper and processed by hand or by means of slow Electromechanical machine. This
device certainly was inadequate hence it failed in face of massive growth in
transactions.
Information
Technology has provided us with very good methods of transacting business, e.g.
West Union Money Transfer operate by First Bank of Nigeria Plc and the use of
point of sale terminals (POS).
MILITARY APPLICATION:
Computer and
Telecommunication technologies have been employed for Military purposes ever
since their beginning-calculation of ballistics of artillery shells and
transmission and decoding messages are among the best-recorded uses of these
technologies. The automated battlefield concept includes Missiles, which find
their pre-programmed target with very high accuracy.
EDUCATION AND TRAINING:
Information
Technology is mostly widely used in broadcasting (Telephone, Radio, etc). Other
areas where IT is applicable are Computer Assisted Training (CAT), Computer
Managed Learning (CML), with training material such as TUTORIAL on a
screen-based terminal. Computer Managed Learning monitors the responses, and
answer to the parts of questions.
The computer
records progress of the learner.
LEISURE:
One of the common use of computer by many
today is for whiling away of time when they are bored with work. There are a
lot of games than one can play with computer system. Most desktops come with
games preinstalled with the operating system and other games can be bought and
installed for leisure hours. One can either play such games with the computer
or play alone or play with some one else and having the computer as the umpire.
COMPUTER AS AN AID TO LAWYER
Computers are used in many law chambers to
record cases and courts proceedings. With Expert system and artificial
intelligence that characterise the fifth generation computers of today,
computers with a well developed database is capable of determining and
revealing various defence strategies based on similar cases that have been
determined somewhere else before.
DATA PROCESSING TECHNIQUE
Data processing systems make use of
one or more processing techniques, depending on the requirements of the
application. The methods can be categorised according to the ways in which data
is controlled, stored and passed through the system; the major categories are:
batch processing; on-line processing, which includes real-time and
time-sharing; distributed processing and centralised processing.
Batch Processing: The Batch processing method process batches of data at regular
interval. It closely resembles manual methods of data handling, in that
transactions are collected together into batches, sent to the computer centre,
sorted into the order of the master file and processed. Such systems are known
as traditional data processing systems. It has advantage of providing many
opportunities for controlling the accuracy of data and conversely, the
disadvantage is the delay between the time of collecting transaction and that
of receiving the result of processing.
On-line Processing System: On-line processing systems are those where all peripherals in use
are connected to the CPU of the main computer. Transactions can be keyed in
directly. The main advantage of an on-line system is the reduction in time
between the collection and processing of data. The two main methods of on-line
processing are real time and time-sharing processing.
Real-time processing: This refers to situation where event is
monitored and controlled by a computer. For example a car's engine performance
can be monitored and controlled by sensing and immediately responding to
changes in such factors like the air temperature, ignition timing or engine
load. Microprocessors dedicated to particular functions are known as embedded
system.
Time Sharing: This refers to the activity of the computer's processor in
allocating time-slices to a number of users who are given access through
terminals to centralised computer resources. The aim of the system is to give
each user a good response time. The processor time-slice is allocated and
controlled by time-sharing operating system.
Distributed Processing
As the term suggests, a distributed
processing system is one which spreads the processing tasks of an organization
across several computer system; frequently, these systems are connected and
share resources (this may relate to common access to files or programs) through
a data communication system. Each computer system in the network should be able
to process independently.
Centralised System
With this type of system, all
processing is carried out centrally, generally by a mainframe computer. This is
achieved through computer networks. There are several networks that is linked
with the central computer where processing takes place.
Multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by having the computer switch rapidly between running each program in turn. One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.
Multiprocessing
Cray
designed many supercomputers that used multiprocessing heavily.
Some computers may divide their
work between one or more separate CPUs, creating a multiprocessing
configuration. Traditionally, this technique was utilized only in large and
powerful computers such as supercomputers, mainframe computers
and servers.
However, multiprocessor and multi-core
(multiple CPUs on a single integrated circuit) personal and laptop computers
have become widely available and are beginning to see increased usage in
lower-end markets as a result.Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers. They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.
DATA
COMMUNICATION AND NETWORKS
Introduction
Communication means an exchange of information between two or more parties and it can be exchange in a variety of way, that might be in the form of word, letters, messages drawing, body movement or any other symbols that represents the idea which make to other understandable. Data communication entails electronically exchanging data or information. It is the movement of computer information from one point to another by means of electrical or optical transmission system. This system often is called data communication networks.
Communication means an exchange of information between two or more parties and it can be exchange in a variety of way, that might be in the form of word, letters, messages drawing, body movement or any other symbols that represents the idea which make to other understandable. Data communication entails electronically exchanging data or information. It is the movement of computer information from one point to another by means of electrical or optical transmission system. This system often is called data communication networks.
Data Communication systems can therefore
be defined as the combinations of facilities including software to aid data
movement from one location to the other electronically:
In today's computing world, data
refers to facts, statistics, pictures, voice and other information that is
digitally coded and intelligible to variety of electronic machines. The key
technology of the information age is computer communications. The value
of high-speed data communication network is that it brings the message sender
and receiver closer together in time. Data communication and networking
is a truly global area of study. It facilitates more efficient use of
computers and improves the day to day control of business by providing faster
information flow. The information society where information and intelligence
are the key drivers of personal, business, and national success has arrived.
Data communication is the principle enabler of the rapid information exchange
and will become more important than the use of computer themselves in the
future. To be more familiar that what is data communication and its
capabilities along with its limitation, we have to be familiar with the data
communication media, components of data communication
Communication media
It is necessary to have a pathway or the media to transmit data from
one point to another. The term media means the device that transmits the voice
or the data form one point to another. Many different types of
transmission media are in use today for example: copper wire, glass or plastic
cables, which are called fiber optic cables or air transmission (radio,
infrared, microwave, or satellite). There are two types of media; one is guided
media and another is radiated.
In Guided media the messages flow through the physical media like
twisted pair-wire, coaxial cable, fiber optic cables, the media guided is the
signal.
In Radiated media messages is broadcast through the air such as
infrared, microwave, or satellite.
Data Transmission and Communication Device
Data is the specific individual facts or the facts, from which
decision can be made; it is the raw facts that can be processed into accurate
and relevant information. Digital and analog is the two types
of fundamental data; Digital and analog transmission have the following
features;
-
computers produce the digital data where as telephone produces analog
data.
-
Digital data are binary
either on or off and the analog data is the sound wave.
-
Analog signals are continuous
waves that carry information by the characteristics of the waves.
Analog transmission is the transmission of a continuously variable signal as
opposed to a direct on/off signal.
-
The traditional way of
transmits telephone signal is an example of analog transmission. Digital signal
is a discontinuous
signal whose various states are discrete intervals apart, such as +15
volts and -15 volts. Most computers transmit the data in a digital form over
the digital circuit to the attached device for example to the "printer"
same as analog voice data also can transmit to the analog form through the
telephone networks.
Data can be
transmitted from one specific form to another. For example; as we know most of
computer produces the digital data; we can convert digital data to analog voice
data by using the special device called MODEM
through the analog telephone circuit.
Data transmission
may be either asynchronous or synchronous.
Asynchronous transmit only one character
at a time and during transmission the character is preceded by a start bit and
followed stop bit that lets the receiving device known where a character begins
and ends. Asynchronous transmission is inherently inefficient due to the
additional overhead required for start and stop bits, and the idle time between
transmissions. It is therefore generally used for only low speed data
transmission.
Synchronous transmission is a form of
transmission in which data is sent as a block using frames or packets. In
Synchronous transmission a group of character is sent to communication link in
a continuous bit stream while data transfer is controlled by a timing signal
initialed by the sending device. Used for high speed transmission.
ON-LINE DATA TRANSMISSION
This means that communication lines
are directly connected to the computer either by means of a multiplexor or
(Transmission controller) or by means of interface unit. The interface unit
scans the communication lines frequently to dictate those that are ready to
send or receive data. When a line is ready to transfer data, the scanning
ceases and the channel number of the line is signalled to the CPU if the
processor is in a position to accept data, then transmission begins.
OFF-LINE DATA COMMUNICATION
This type of data transmission
indicates that the communication lines are not connected directly to the
computer. Key-to-disk are often used for off-line preparation and transmission
of data in remote job-entry-system.
ELEMENTS OF DATA COMMUNICATION
(a) Information Source
(b) Message
(c) Transmitter (d) Signal
(e) Receiver
(f) Information Destination
Information Source: Originator of messages wishing to convey information to another
person.
Message: This is the idea/information that the sender wants to pass across
to the receiver at a particular destination.
Transmitter: Wireless operator transmitting messages by means of a mouse key
connected to transmitting set.
Signal: The signal produced by the transmitting set when the mouse key is
depressed.
Receiver: Wireless operator receiving message by means of a receiving set.
Information Destination: Receipt of, message by addressee.
EQUIPMENT/COMPONENTS REQUIRED FOR
DATA TRANSMISSION
(a) Multiplexor (b)
Front-End-Processor (c) Concentrator (d) Modem
Modems
MODEM Stands for MODulator DEModulator is used to convert analogue signal to digital and vice versa. A modem is a device that modulates and demodulates the signals. Modulation means the conversions of data from digital signal to analog signal and demodulates means the conversion of data signal from analog to digital signal. Modems are always use in pairs. The unit at the sending end converts the digital signal to analog signals for transmission through the analog circuit; at the receiving end, another modem converts analog to digital for the receiving computer. Modem transmission rate is measured in bits-per-second and it usually expresses bps. The amount of data actually transferred for one system to another is depends upon the speed of the modem.
MODEM Stands for MODulator DEModulator is used to convert analogue signal to digital and vice versa. A modem is a device that modulates and demodulates the signals. Modulation means the conversions of data from digital signal to analog signal and demodulates means the conversion of data signal from analog to digital signal. Modems are always use in pairs. The unit at the sending end converts the digital signal to analog signals for transmission through the analog circuit; at the receiving end, another modem converts analog to digital for the receiving computer. Modem transmission rate is measured in bits-per-second and it usually expresses bps. The amount of data actually transferred for one system to another is depends upon the speed of the modem.
Front-End Processor (FEP): A front-end
processor is the special purpose device; this specialized computer manages all
routing communications with peripheral devices. For large mainframe
installations, a front-end processor is typically a special purpose
minicomputer. The primary application of the FEP is to serve as the interface
between the host/client computer and the data communication network with its
thousands of terminals or microcomputers. It can handle coding and decoding
data, error diction, retrieval of message, interpreting, and processing of the control
information, addressing, routing message to the right computer, and breaking
the long message in to small packets. Front-end processor can provide up to 30
percent additional processing time for mainframe.
Multiplexors
Multiplexors is an electronic device that allows a single communications channel to carry data transmissions simultaneously from many sources. Multiplexing a data communication means that two or more information is sent simultaneously via the communication circuit. Multiplexors is transparent, when the circuits are multiplexed at one end and demultiplexed at the other, each user's terminal or microcomputer thinks it has its own separate connection to the host computer. The objective of multiplexor is to reduce communication costs by allowing the more efficient use of circuits through sharing.
Multiplexors is an electronic device that allows a single communications channel to carry data transmissions simultaneously from many sources. Multiplexing a data communication means that two or more information is sent simultaneously via the communication circuit. Multiplexors is transparent, when the circuits are multiplexed at one end and demultiplexed at the other, each user's terminal or microcomputer thinks it has its own separate connection to the host computer. The objective of multiplexor is to reduce communication costs by allowing the more efficient use of circuits through sharing.
TYPES OF TRANSMISSION
Simplex Channel: In this type of communication, transmission takes place in one
direction. The system known as Teletex, the sending of data alongside a
television signal, is a good example of a simplex channel. Here the recipient
has no formal means of communicating with the originator to ask for a repeat if
there is an error
Half-Duplex: This communications is bi-directional, but transmission moves in one
direction at a time. The example is in radio telephone conversation. A protocol
using the word "over" to allow the direction of data flow to change
is used.
Full- Duplex: this allows bi-directional communication simultaneously. This is
used for normal telephone conversation where both the initiator and the
receiver can talk at the same time.
NETWORKS
An interconnected set of two or more
computers may be called a "Computer Network". A computer that is not
connected to other computers is a "Stand-alone system".
Basic Advantages of Using Networks
There are many possible advantages
in using networks. The basic ones are:
a. the sharing of resources (e.g.
computers and staff) and information.
b. The provision of local facilities
without the loss of central control
c. The even distribution of work d.
Improved communication facilities
CATEGORIES OF NETWORKS
Networks can be grouped into three.
They are; Local Area Network, Metropolitan Area Network and Wide Area Network.
Local Area Network (LAN): this is the network of computer that provides coverage within a
building. Computers within an office or building are interconnected to share
information. Here no public regulatory body's permission is required for the
connection.
Metropolitan Area Network (MAN): These are networks that cover a city. It can be seen as various LAN
connected within a city to share information. Here public regulatory body's
permission is required.
Wide Area Network (WAN): These are networks that cover nation and international.
COMPONENTS OF NETWORK
There are three basic hardware components for a data communication
network:
Server or host computer: A server is a machine that provides clients with service. Servers share a specific resource with other computers. Examples of the servers are the database server, that provides the large database and the communication server that provides connection to another network, to commercial database, or to a powerful processor. There are file, database, network, access, modem, facsimile, printer, and geteway server. Servers are usually microcomputers (often more powerful than the other microcomputers on the network), but they may be minicomputers or mainframes.
Server or host computer: A server is a machine that provides clients with service. Servers share a specific resource with other computers. Examples of the servers are the database server, that provides the large database and the communication server that provides connection to another network, to commercial database, or to a powerful processor. There are file, database, network, access, modem, facsimile, printer, and geteway server. Servers are usually microcomputers (often more powerful than the other microcomputers on the network), but they may be minicomputers or mainframes.
Client: A client is a computer such as a PC or a workstation attached to the network, which is used to access shared network resources. Client computer uses the resources shared by server computer. There are three major categories of clients: terminals, minicomputers/workstation, and special purpose terminals.
Circuit: The circuit is the pathway through which the message passes. Circuits can be twisted pair cable, coaxial cable, fiber optic cable, microwave transmission, and so forth. There are many devices in the circuit that perform special functions, such as hubs, switches, routers and gateways.
NETWORK TOPOLOGIES
Computer networks can be categorized
according to their physical shape or topology. Each terminal in a network is
known as a node. If a central computer controls the network it is known as the
host computer. The topology of a network is the arrangement of the nodes and
the ways they are interconnected. The communication system within a network is
known as the subnet. The various network topologies are;
Star topology: this means that each node is connected, by separate connections to a
computer at the centre. The star is a popular topology for WAN.
Star
topology
Ring Topology: this is specifically designed to use with LAN. Here all the nodes
are connected in a ring form as illustrated below. Messages in ring network
flow in one direction, from node to node in anticlockwise. The ring consists of repeaters, which are
joined by the physical transmission medium. They have no host and none of the
nodes need have overall control of access to the network.
Ring Topology
Bus Topology: With bus topology, the workstations are connected to main cable
(known as the bus or trunk), along which data travels. The ends of a bus are
not connected, so that data has to travel in both directions to reach the
various nodes on the network. The main bus standard is known as Ethernet. The
term station tends to be used rather than node for this type of network.
Bus topology
INTERNET BASICS
Internet
is an international network of networks of computers linking different types of
users: Academic, Industries, Government, Health Institutions, military,
individuals, etc, for the purpose of sharing information. As a communication
network among computers, the internet allows you to locate and retrieve
information on other computers linked to he internet as well as send messages
electronically to and from other people elsewhere on the internet. Whenever
Internet software application is used, the client software will either be on
your personal computer, the computer you log onto for access to the internet
(your host), or yet another computer to which you connect in other to use
client software you may not have on your computer. As you navigate through the
Internet, you will find yourself logged onto different host computers,
sometimes gaining access to different client programs and also accessing
different servers; it can be complicated. Fortunately, the purpose of advanced Internet software is to hide these complexities from users
so as to achieve success.
The internet has six application
protocols: Electronic mail (E-mail), World Wide Web (Hypertext Transfer
Protocol or HTTP), Gopher, Telnet, File Transfer Protocol (FTP), Each of these
application protocol has special client software, and many web browsers, such
as Netscape from communication and internet Explorer from Microsoft, which are
capable of reading and displaying data from all the applications.
BENEFITS OF INTERNET APPLICATION
(a) Downloading of information
(b) Advertisement
(c) Accessing newspapers, magazines
and academic journals
(d) On-line banking
(e)
Accessing international media (CNN, BBC, VOA)
USES OF THE INTERNET
The various uses of the Internet
are;
Electronic Mail (E-MAIL): E-mail is a method of
sending messages back and forth among people with Internet addresses as well as
on other networks with mail addresses or connections to the Internet. The main
common features are that the messages are converted to electrical signals for
the purpose of transmission. It is primarily an alternative to the conventional
postal service.
Electronic mail is one of the most
useful features of the Internet and it is often the application with which
people begin. As a means of sending messages back and forth among people with
internet address as well as people on other network with mail connections to
the internet, the E-mail support both person to person communications (that is
delivered to the electronic address of the intended recipient) and one to many
transmission in which information is automatically sent to a list of people.
Comparison between E-Mail and Postal Mail
E-mail
Postal
mail
(a) Faster
Slow
(b) Efficient
Inefficient
(c) Uses
telephone line Message
travels through road, air or sea
(d) Medium
of message is electronic Medium of
message is Paper
World Wide Web (WWW): World Wide Web is the most exciting new tool for the Internet. It
is based on the technology called hypermedia. With hypermedia, information in
one document can be linked to another; related information can consist of not
only text but graphics, audio and video information as well. WWW is an
ambitious, exciting and powerful attempt to link connected information wherever
it may be located on the Internet, allowing the user to easily access and
retrieve related files
TELNET: Telnet allows you to log on to another computer on the net. The
computer onto which you are logging is known as remote computer. Once you are
logged onto a remote computer, it becomes as if your keyboard was attached to
that computer, which then serve as your host. You can do whatever the people
are regularly attached to the computer can do. It is also possible that the
computer you currently using to access the Internet that does not have the
client software with which you want to work, you can use Telnet to log onto
another computer on the internet that does not have the right tools.
File Transfer Protocol (FTP): File
transfer protocol has the facilities that can be used for moving files from one
computer to another. It is the common language for sharing data. Unlike Telnet, in which
you must often know a specific password to successful log onto the remote
computer, anonymous FTP has become a common place. With anonymous FTP, anyone
on the Internet may transfer files from
and sometimes to a remote system using the word anonymous as the
user identification.
USENET:
Usenet is a network of several
thousands online bulletin organized into topic-oriented "news group".
Within these news groups, people read and post related messages. There are
already more than 10,000 news groups with participants ranging from computer enthusiasts to music
composers. Usenet is one of the many networks connect to and accessible through
the Internet.
Gopher
Gopher was the first program to
investigate the information search and retrieval processes on the Internet.
Like other Internet applications, Gopher consists of servers and client
software. More than 2,000 gopher servers have been linked. When you find
something that you want, the client software retrieves it for you through
menu-based commands. With Gopher, it does not matter where exactly the
information you want is located. It does not matter, what kind of information
you want to retrieve. Nor does it matter what tool you need to use to retrieve
that information. You use tool from the menu to perform each operation.
MICROSOFT WINDOWS '95/98/Me/Xp
Microsoft Windows '95/98/Me is a recent most powerful
operating system that affords users much capability in the overall usage of the
computer systems. It completely transforms the way the computer is being used.
Microsoft Windows '95/98/Me offers the following among others:
ability to run more than one
application at a time.
ability to transfer information
between applications.
provision of an efficient work
environment for your PC.
presentation of a super graphical
interface, which makes computer usage simple for the user.
Microsoft Windows is a software that is user-friendly,
provides an on-line tutorial, and extensive context-sensitive online help
system. In order to enjoy the windows software, a mouse is required (though,
not mandatory) and most of our discussions would assume that our computer
system is equipped with such peripheral.
Starting Windows 95/98 is easy. If your computer uses a Windows 95/98
operating system, it starts
automatically when you turn on the computer.
Ending Windows 95/98 is also straightforward
— here’s how you do it..
First, click on the Start button 
in the
lower left-hand corner of your computer screen.
Next click on Shut Down.
in the
lower left-hand corner of your computer screen.
Next click on Shut Down.
Figure 1 - Windows Start Menu
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A Shut Down Windows dialog box will appear as shown in Figure
1. Select the first option, Shut down the computer by
selecting the button shown below. Your computer will now begin to shut
down. You can turn off the power switch
when the orange or red writing appears saying “It’s now safe to turn off your computer.”
Figure 2 - Windows shut down dialog box
Tip
 |
When shutting your computer, please
follow the steps listed above. Just
turning off the computer without exiting Windows first could corrupt your
files.
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2. Your desktop
Windows 95/98/Me uses the metaphor of a
desk. On the top of your desk you have
the main tools you work with -- your pen, paper and other items. The same applies
to the Windows 95/98/Me operating system. You have your main tools on the
screen of your monitor as shown
below. Windows 95/98/Me calls
this your desktop.
Figure 3 - The
Windows 95/98/Me Desktop
The mouse makes it easier to use Windows
and Windows-based software. It is
therefore essential that you know how to
use your mouse.
Four types of mouse actions
The four types of mouse actions are
described below.
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Action
|
Description
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Example
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Configuring your mouse
You
can modify, or configure how your mouse functions. To do this, left click on the Start button. Select Settings, Control
Panel. Select the image of the mouse from the icons. You can make changes to buttons, pointer and
motion here. For example, if you are left handed, you might prefer to place the
mouse on the left side of your keyboard and select the right mouse key for
clicking. Or if you find it difficult to find the mouse pointer, you might
decide to make it larger, by selecting pointers.
The desktop appears when you turn on your
computer. You can launch a program from
the desktop by double clicking on the icon of the program you wish to start. If
you don’t see the desktop it is probably because you have programs open. In this case
you can launch programs by clicking on the Start button on the bottom left corner of your screen. Move the cursor to Programs on the pop-up menu and a list of possible programs
will appear. Single click on the one you
wish to launch.
Figure 4- Launching
programs from the pop-up menu in Windows
Opening a program from the task bar
Once programs are opened, they appear on
the task bar at the bottom of your screen.
To maximise these programs, simply click on the buttons on the bottom of
your screen. To open a window from the
task bar click on an item. If the task
bar does not appear, select Ctrl + Tab and it will appear.
Figure 5 -
Using the task bar to open and close programs
Parts of a window
Every window in Windows has similar
characteristics. Understanding how one
of these widows functions helps you to learn any Windows application.
Switching between programs
To switch from one open window to another
click on the desired window’s icon and name on the task bar at the bottom of
the screen. Or if you prefer using the
keyboard you can switch between your open windows by holding down the Alt key and selecting the Tab keys.
Figure 6 -
Parts of a window
Maximising and minimising windows
|
A window can
occupy all the screen on your monitor or part of it. If you ‘maximise’ a window it occupies the
entire area. To maximise a window,
carefully click on the small maximise button in the upper right hand corner.
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 |
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If there is not a
maximise button on your screen, the window is already as large as it
gets. To shrink the window click on
the restore button. Now you can
select, the maximise button to make the window larger.
|
 |
|
The minimise
button removes the window from the screen.
Selecting the minimise button does not close the program. It is still available by clicking on the
button on the Task Bar at the bottom of your screen.
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 |
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The close button closes the program
or window.
|
 |
Scroll bar
If the information you are viewing does
not fit completely on one screen, you can see more by using the vertical and
horizontal scroll bars. When there is no
scroll bar on your screen, there is no additional information to access.
Figure 7 -
Using the task bar to access help
Once help is open, you can use the Find tab to locate help on the topic
you need.
The Help
function is a rich source of information and useful tips. Once you open
the Help
dialogue box, you can either type the information you are looking for in
the Find tab (as shown in Figure 9) or locate it by scrolling through the Contents or Index tabs. To locate a specific topic using the Find tab for example, select Help on the Taskbar’s Start
Menu. Select the Find tab. Type in one word for the topic that interests
you. Type ‘help’ for example. If you type help 140 topics appear. You
can select the ones that match your interest.
Figure 8 -
Using the find tab to list 140 help items
Multitasking
is the process of performing two or more computer tasks at the same time. For
example you might be printing a document in Microsoft Word while you are
checking your email in Eudora at the same time.
To
perform the multitasking action mentioned above, you would first of all send a
document to the printer. Secondly you would switch to the Eudora application,
either by launching it or by using the switch to feature. You can switch to another open software
package by holding down the alt key
and pressing tab or by selecting the software package from the task
bar.
The
multitasking feature allows you to be more productive; however you must
exercise caution. Each application and
each file uses computer resources. You
may experience computer slow downs and even failure when you have an excessive
number of applications open. Therefore,
we strongly urge you to limit the number of applications you have open.
One
of the most useful features of Windows is the ability to place a portion of one
document into another. Although there are many ways to do this, the copy and
paste feature is one of the easiest ways to place text from one document into
another.
Copy
and paste is particularly helpful when you are composing email messages. Using
this method, you can, for example, compose your message in your word processing
software using the writing tools to check your spelling and your grammar. Next copy and paste the text into an email
message. You can also use this feature to copy text from one email message into
another.
If
you wish to copy only a portion of a document, you can do this by following
these steps: First, highlight the text you wish to copy by placing the cursor
at the beginning of the text, clicking on the left mouse button, and dragging
your mouse until the end of the text you want copied. The selected text should now be
highlighted. Next, press Ctrl
+ C. This will copy the text to the Windows clipboard. Next, place the cursor in the new document
where you would like to place the text.
Press Ctrl + V, and this will
paste the text into the new document. You can also copy graphics from one
location to another in the same manner.
If
you wish to copy the entire document, you can easily do so by pressing Ctrl + A.
This will highlight the entire document. To copy it to the Windows
“clipboard”, press Ctrl + C. Move
your cursor where you want the document to be pasted and Press Ctrl + V.
Files contain computer data, whether it
be the messages of your email, the
columns of numbers of your spread sheet, or the computer programs that run your
software. Over time, you may accumulate a large number of files and locating
files may become difficult.
Files can be grouped together in
folders. Organising your files by
type, project, or some other convention
helps you manage your data.
The key to managing files is Windows
Explorer. The basic tasks you perform in
managing your files are: viewing files, setting up folders, copying, naming and
sorting. We take a closer look at these below.
Discovering Windows Explorer
Where did my file go? How can I be certain that I am accessing the
latest version of a file? Where can I
store valuable information? Windows
Explorer helps answer these questions and others.
|
Questions
|
Answers
|
|
1. What is Windows
Explorer?
|
Windows Explorer maps your computer,
showing what is in all drives and other pertinent information.
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|
2. Why use it?
|
You can
use Windows Explorer to see all the folders and files on your computer. That way you can manage all your
information.
|
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3. How
do I access it?
|
A fast way to access Window Explorer is
on the Start menu. Right click on the start button and then
select Explore.
|
Viewing files
Windows Explorer gives you a convenient
way to view your folders and files.
After you have launched Windows Explorer, the easiest way to see a list
of your files is to choose a folder in the left panel and left single-click on
it. This will produce a list of folders
and files — in the right panel. These
are the files or folders contained in the folder you clicked on.
Tip
|
|
If the files and folders appear in the
right panel, it is because you double-clicked on the folder you chose in the
left panel.
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Setting up folders
Windows 95/98/Me stores files in
folders. In Windows 3.x and DOS we
called these directories. You can decide
which folder a file gets stored in.
Setting up folders, logically named, and easy to find allows you to
quickly find and retrieve your work. A
good, but not the only way to set up folders is to use Windows Explorer. To do this, select File, New,
Folder. When New
Folder appears in your Explorer Window, type in the name you decide to call
the folder.
Figure 9 -
Creating a new folder in Explorer
Copying files
Right click on
the file you want to copy. (Its colour
will change to show it is selected.) A
pop-up menu will appear. Select Copy from the pop-up menu. Still using Windows Explorer select a new
drive and or folder for the file by clicking once. In the right-hand panel, right click on an
open space (not a file name line) and select Paste from the pop-up menu. You can check if the file has been
successfully copied by opening the folder in which you tried to place it and
checking if the file is there.
Figure 10-
Folders on a computer as viewed in Windows Explorer
Naming and renaming files and folders
If you are working with use Windows 95/98/Me
only, you can use longer, more explicit file names than you can use in DOS or
Windows 3.1. You can easily rename files
in Windows Explorer by right clicking on a file or folder you wish to rename
and selecting Rename from the pop-up
menu.
Windows 95/98/Me allows you to save a
file using up to 255 characters. However, it is recommended that you limit your
file name to 8 characters to make it easy to share files with those who do not
work with Windows 95/98/Me. Each file can have an extension. The extension is the three last characters in
the file name which follow the period.
When you are saving a file, many software packages will automatically
add the correct extension for you. For
example, if you are saving an HTML file from the Internet, your Web browser
will add the ‘htm’ extension to the end of the file name. Or, if you are saving a file in Word, the
software will automatically add the ‘doc’ extension to the end of the file
name.
Files ending in ‘exe’ are program files
that ‘execute’ software applications.
Sorting files
Windows
Explorer allows you to sort your files by name, size, type or date. You
can do this by selecting View from
the Windows Explorer menu and then selecting Arrange Icons from the pop up menu. This is particularly useful for
finding the latest version of a file.
Once you have found that file, you can click on it and if it has an
extension that Windows 95/98/Me understands, the associated software will
automatically launch and open the file you selected. You can start working in
the file immediately.
If
you do not know how to create a
document, here is an exercise to help you.
Although you will probably create your documents in word processing
software like MS Word or WordPerfect, we are asking you to use WordPad, an
introductory level word processing software that everyone receives with Windows
95/98/Me. If for some reason you do not have WordPad, or you prefer to use
another software package, the following instructions will nevertheless provide
useful guidelines.
Open
WordPad, by selecting the Start button,
Programs, Accessories. Type a short message in
the WordPad window. Select File, Save As. The Save As window will
appear. If you do not specify the folder in which you wish to save your file,
windows will save the file in a default folder. If you want to save it in
another folder, select the folder now. Type the file name and click the Save
button. If you save the file now, it will save in a default folder. It is
better to set up a folder and file for this purpose. In Windows 95/98/Me the terms ‘folder’ and
‘directory’ are used interchangeably.
The
steps in creating folders and naming a file are as follows. Click on the Up One Level icon shown in the
following diagram until you come to the C
drive. At this level you might notice a folder with a name like My files or My documents, that your software has generated automatically. If
you do not notice a folder like this, you can create one, by using the Create New Folder icon. It is to the
right of the Up One Level icon. To
name a new folder, type the name of the folder into the naming area over top of
the words New Folder. You can do
this when the letters are white on a blue background. Once you have selected
the correct folder, you can name your file and save it, using information
explained below.
Figure 11Using the Save As dialog box
Why save files
If you wish to keep an electronic copy of
your document or data, you must save it before you close the application. You
could save files shortly after you start writing them and throughout the
process. A good short cut for saving is Ctrl + S. Once saved, a file can be
retrieved for viewing or editing. You can also send it to another person.
Questions
|
Answers
|
|
1. Where do I save files?
|
Decide the folder in which you want to
save the file. If you do not want to save the file in the default folder,
create a new folder that explicitly describes the subject. Select a name that
you can easily remember..
|
|
2. How do I
save files?
|
Use the save feature in your software found
under the File menu.
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3. What should
I name the files?
|
Choose a name that most describes your
file and that you can easily remember. Windows 95/98/Me allows you to use up
to 255 characters to name your file. However, it is advisable that you limit
your file name to 8 characters to make it easily accessible to those that do
not use Windows 95/98/Me. You can use blank spaces to separate words in the
file name.
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4. What
characters can I not use?
|
\ /: *? “ ‘ < > and | are
forbidden.
|
|
5. What about
extensions?
|
You can add a three-letter extension. Alternatively, you can let the software do
it. Normally, it works well to let the
software decide.
|
|
6. How do I find the files
after saving them?
|
Use Windows Explorer as described above
in Chapter 8. Managing Files.
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Tip
 |
In Windows 95/98/Me, you can use 255
characters in a file name. In Windows
3.x, the maximum is eight characters. If a file with a name longer than eight
characters is imported into Windows 3.x, the software will automatically
reduce the number of characters in the name to eight — sometimes making it
almost impossible to distinguish between files. The solution is simple. If you are saving a file that will
eventually be used in Windows 3.x, do not exceed 8 characters in the name.
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A mouse is a handy tool for selecting an
action from a menu. However, there are also keyboard shortcuts that let you
perform the same tasks.
For example, in Windows95/98/Me WordPad,
to create a new document, you move the mouse pointer to New icon which is represented by an icon of a blank sheet of
paper. You can also perform the same
function by holding down the Ctrl key and selecting the N key.
We write this as Ctrl + N. This is faster since it performs the same
action with one step, compared to several steps with the mouse.
Here are a few shortcuts that work in
most Windows software.
|
Select
|
And you will . . .
|
|
1. Alt
+ F4
|
exit the current program
|
|
2. Alt
+ Tab
|
switch to the previous application
|
|
3. Alt
+ Tab + Tab
|
scroll through the list of open software
applications
|
|
4. Ctrl
+ Esc
|
show the start up menu and task bar if it
is hidden
|
|
5. Ctrl
+ A
|
select all the text and graphics in the
document on the screen
|
|
6. Ctrl
+ C
|
copy the selected area
|
|
7. Ctrl
+ P
|
print the document on the screen
|
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8. Ctrl
+ S
|
save the document on the screen
|
|
9. Ctrl
+ V
|
paste or insert the text you have copied
or cut
|
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10. Ctrl
+ X
|
cut (remove) the selected text
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11. Ctrl
+ Z
|
undo the previous action
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12. Del
|
delete the selected area or the single
closest character to the right
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13. Esc
|
close a dialog box
|
|
14. F1
|
get help in a program or dialog box
|
|
15. Shift
+F10
|
View a shortcut menu for a selected item
or area; next you can use your down arrow to select an item. This gives you access to the right mouse
button features without touching the mouse!
|
Backups are important to ensure that you
have access to important data in the event that the data stored on your
computer is damaged or lost.
You can backup onto various devices
(media). Backing files up to floppy
disks is probably the most common technique for dealing with small amounts of
data. For larger amounts of data such as
entire hard drives, you may wish to consider using a tape backup or if you are
connected to a Local Area Network (LAN) you may be able to backup to a server.
The procedure described below for backing
up your files works with both a stand-alone personal computer and a local area
network or LAN. If your computer is connected to a LAN, please check with your
system administrator about local procedures for making a backup.
There are various backup programs
available. To use the backup program
that comes with Windows 95/98/Me, select Help
from the start-up toolbar, next select Find,
type ‘backup’, select the first
item Accessories: using backup to backup
your files.
You can also select backup from the
start-up toolbar by selecting Programs,
Accessories, Systems Tools, Backup. When you do that you will come to the dialog
box shown blow. Select the type of backup
you would like to do here.
You can obtain additional information
about how to use Backup, by clicking on the Help menu in Backup.
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