introduction to computers-comprehensive

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INTRODUCTION TO COMPUTERS

A: INTRODUCTION

1. What is a computer?

A computer is an information-processing machine. It may also be defined as a device that

works under the control of stored programs automatically accepting, storing and

processing data to produce information that is the result of that processing.

The forms of information processed include:

Data – e.g. invoices, sales ledger and purchase ledger, payroll, stock controls etc.

Text – widely available in many offices with microcomputers

Graphics – e.g. business graphs, symbols Images – e.g. pictures

Voice – e.g. telephone

Processing includes creating, manipulating, storing, accessing and transmitting.

DATA

Groups of non-random symbols that represent quantities, actions, objects etc. Data items are formed from characters that may be alphabetical, numeric, or

special symbols.

Data items are organized for processing purposes into data structures, file

structures and databases.

Data relevant to information processing and decision-making may also be in the

form of text, images or voice.

INFORMATION

Data that has been processed into a form that is meaningful to the recipient and isof real or perceived value.

Data for one level of an information system may be information for another. For

example, data input to the management level is information output of a lower level

of the system such as operations level.

Desirable qualities of information

1. Availability – Information should be available and accessible to those who need it.

2. Comprehensible – Information should be understandable to those who use it.

3. Relevance – Information should be applicable to the situations and performance of

organizational functions. Relevant information is important to the decision maker.4. Secure – Information should be secure from access by unauthorized users.



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3. Why use computers?

Use of computers has become a necessity in many fields. Computers have revolutionized

the way businesses are conducted. This is due to the advantages that computer systemsoffer over manual systems.

The advantages include:

Speed – Computers have higher processing speeds than other means of processing,measured as number of instructions executed per second.

Accuracy – Computers are not prone to errors. So long as the programs are correct,

they will always give correct output. A computer is designed in such a way that

many of the inaccuracies, which could arise due to the malfunctioning of the

equipment, are detected and their consequences avoided in a way, which is

completely transparent to the user.

Consistency – Given the same data and the same instructions computers will produce exactly the same answer every time that particular process is repeated.

Reliability – Computer systems are built with fault tolerance features, meaning thatfailure of one of the components does not necessarily lead to failure of the whole

system.

Memory capability – A computer has the ability to store and access large volumesof data.

Processing capability – A computer has the ability to execute millions ofinstructions per second.

4. Computer application areas

Some of the areas that computers are used include:

Communication – digital communication using computers is popular and is beingadopted worldwide as opposed to analogue communication using the telephony

system. Computers have also enhanced communication through email

communication, electronic data interchange, electronic funds transfer, Internet etc.

More specific examples include:

Banking – the banking sector has incorporated computer systems in such areas ascredit analysis, fund transfers, customer relations, automated teller machines, home

banking, and online banking.

Organizational management – the proliferation of management information

systems have aided greatly the processes of managerial planning, controlling,

directing as well as decision-making. Computers are used in organization for

transaction processing, managerial control as well as decision-support. Otherspecific areas where computer systems have been incorporated include sales and

marketing, accounting, customer service etc.

Science, research and engineering – computers used

o as research tools, complex computations

o for simulation e.g. outer-space simulations, flight simulations

o as diagnostic and monitoring tools,



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o computerized maps using global positioning satellite (GPS) technology

o for modern mass production methods in the auto industry using computer

driven technology

Education – computers incorporate databases of information that are useful inorganizing and disseminating educational resources. Such E-learning and virtual ordistributed classrooms have enabled the teaching industry to have a global reach to

the students. Computers are also used for test scoring uniform tests done in

schools, school administration and computer aided instructions.

Management of information materials- The Internet has massive reference

material on virtually every learning area. Computer systems have enabled the

efficient running of libraries for information storage and retrieval.

Manufacturing and production – computer aided design (CAD), computerintegrated manufacturing (CIM), process control systems among other

technologies are computer systems that have revolutionized the production

industry.

Entertainment – use of computers in the entertainment industry has increasedtremendously over the years. Computers enable high-quality storage of motion pictures and music files using high-speed and efficient digital storage devices such

as CDs, VCDs and DVDs. The Internet is also a great source of entertainment

resources. Computer games have also become a major source of entertainment.

Retailing – computers are used in point of sale systems and credit card paymentsystems as well as stock inventories.

Home appliances – computers (especially embedded computers ormicroprocessors) are included in household items for reasons of economy and

efficiency of such items. Major appliances such as microwave ovens, clotheswashers, refrigerators and sewing machines are making regular use of

microprocessors.

Reservation systems – guest booking, accommodation and bills accounting usingcomputers in hotels have made the process to be more efficient and faster. Airline

computer reservation systems have also enhanced and streamlined air travel across

major airlines. Major players in the industry have also adopted online reservation

systems.

Health care and medicine – computers have played an important role in thegrowth and improvement of health care that the use of computers in medicine has become a medical specialty in itself. Computers are used in such areas as

maintenance of patient records, medical insurance systems, medical diagnosis, and

patient monitoring.



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5. History of ComputersThe first electronic computers were produced in the 1940s. Since then, a series of

breakthroughs in electronics have occurred leading to great improvements in the capacity,

processing speed and quality of computer resources.

The evolution of computerization in business may be summarised as:

1870s: Development of the typewriter allows speedier communication and lesscopying.

1920s: Invention of the telephone enables both Wide Area Networks (WAN) and

Local Area Networks (LAN) communication in real time. This marks the beginning of

telecommunication.

1930s: Use of scientific management is made available to analyse and rationalise.

1940s: Mathematical techniques developed in World War II (operations research) are

applied to the decision making process.

1950s: Introduction of copying facilitates cheap and faster document production, andthe (limited) introduction of Electronic Data Processing (EDP) speeds up large scale

transaction processing.

1960s: Emergence of Management Information Systems (MIS) provides backgroundwithin which office automation can develop.

1970s: Setting up of telecommunication networks to allow for distant communication between computer systems. There is widespread use of word processors in text editing

and formatting, advancement in personal computing- emergence of PCs. Use of

spreadsheets.

1980s: Development of office automation technologies that combine data, text,graphics and voice. Development of DSS, EIS and widespread use of personal productivity software.

1990s: Advanced groupware; integrated packages, combining most of the office work-

clerical, operational as well as management.

2000s: Wide spread use of Internet and related technology in many spheres oforganisations including electronic commerce (e-commerce), e-learning, e-health

Landmark Inventions

~500 B.C. - counting table with beads ~1150 in China - ABACUS - beads on wires 1642 Adding machine - Pascal

1822 Difference machine/Analytic Engine - design by Babbage

1890 Holerith punched card machine - for U.S. census

1944 Mark I (Harvard) - first stored program computer 1947 ENIAC (Penn)- first electronic stored program computer 1951 UNIVAC - first commercial computer; 1954 first installation 1964 IBM - first all-purpose computer (business + scientific)

1973 HP-65, hand-held, programmable ‘calculator’

~1975 Altair, Intel - first Micro-computer; CPU on a “chip”



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6. Computer Generations

The view of computers into generations is based on the fundamental technology

employed. Each new generation is characterized by greater speed, larger memory capacityand smaller overall size than the previous one.

First Generation Computers (1946 – 1957)

Used vacuum tubes to construct computers.

These computers were large in size and writing programs on them wasdifficult.

The following are major drawbacks of First generation computers.

o The operating speed was quite slow.

o Power consumption was very high.

o It required large space for installation.

o The programming capability was quite low.o Cumbersome to operate – switching between programs, input and

output

Second Generation Computers (1958 - 1964)

Replaced vacuum tubes with transistors.

The transistor is smaller, cheaper and dissipates less heat than a vacuum tube.

The second generation also saw the introduction of more complex arithmetic

and logic units, the use of high – level programming languages and the provision of system software with the computer.

Transistors are smaller than electric tubes and have higher operating speed.They have no filament and require no heating. Manufacturing cost was also

lower. Thus the size of the computer got reduced considerably.

It is in the second generation that the concept of Central Processing Unit(CPU), memory, programming language and input and output units were

developed. The programming languages such as COBOL, FORTRAN were

developed during this period.

Third Generation Computers (1965 - 1971)

Had an integrated circuit.

Although the transistor technology was a major improvement over vacuumtubes, problems remained. The transistors were individually mounted in

separate packages and interconnected on printed circuit boards by separatewires. This was a complex, time consuming and error-prone process.

The early integrated circuits are referred to as small-scale integration (SSI).Computers of this generation were smaller in size, lower cost, larger memoryand processing speed was much higher.



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Fourth Generation Computers (1972 - Present)

Employ Large Scale Integrated (LSI) and Very Large Scale Integrated (VLSI)

circuit technology to construct computers. Over 1,000 components can be placed on a single integrated-circuit chip.

Fifth Generation Computers

These are computers of 1990s

Use Very Large Scale Integrated (VLSI) circuit technology to build computers.Over 10,000 components can be incorporated on a single integrated chip.

The speed is extremely high in fifth generation computer. Apart from this it can perform parallel processing. The concept of Artificial intelligence has been

introduced to allow the computer to take its own decision.

7. Classification of computers

Computers can be classified in different ways as shown below:

Classification by processingThis is by how the computer represents and processes the data.

a) Digital computers are computers which process data that is represented in the form

of discrete values by operating on it in steps. Digital computers process datarepresented in the form of discrete values like 0, 1, 2. They are used for both

business data processing and scientific purposes since digital computation results ingreater accuracy.

b) Analog computers are used for scientific, engineering, and process-controlled

purposes. Outputs are represented in the form of graphs. Analogue computers

process data represented by physical variables and output physical magnitudes in

the form of smooth graphs.

c) Hybrid computers are computers that have the combined features of digital and

analog computers. They offer an efficient and economical method of working out

special problems in science and various areas of engineering.

Classification by purposeThis is a classification by the use to which the computer is put.

a) Special purpose computers are used for a certain specific function e.g. inmedicine, engineering, manufacturing.

b) General-purpose computers can be used for a wide variety of tasks e.g.

accounting, word processing

Classification by generationThis is a time-based classification coinciding with technological advances.

The computers are categorized as First generation through to Fifth generation.



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a) First generation. Computers of the early 1940s. Used a circuitry of wires and

vacuum tubes. Produced a lot of heat, took a lot of space, were very slow and

expensive. Examples are LEO 1 and UNIVAC 1.

b) Second generation. Computers of the early 1950s. Made use of transistors and thuswere smaller and faster. (200KHz). Examples include the IBM system 1000.

c) Third generation. Computers of the 1960s. Made use of Integrated Circuits.Speeds of up to 1MHz. Examples include the IBM system 360.

d) Fourth generation. Computers of the 1970s and 1980s. Used Large Scale

Integration (LSI) technology. Speeds of up to 10MHz. Examples include the IBM4000 series.

e) Fifth generation. Computers of the 1990s. Use Very Large Scale Integration

(VLSI) technology and have speeds up to 400MHz and above.

Classification by power and size/ configuration

a) Supercomputers. The largest and most powerful. Used to process large amounts ofdata very quickly. Useful for meteorological or astronomical applications.

Examples include Cray and Fujitsu.

b) Mainframe computers. Large computers in terms of price, power and size.Require a carefully controlled environment and specialist staff to operate them used

for centralized processing for large commercial organizations. Manufacturers

include International Business Machine (IBM).

c) Minicomputers. Their size, speed and capabilities lie somewhere between

mainframes and microcomputers. Used as departmental computers in large

organizations or as the main computer in medium-sized organizations.Manufacturers of minicomputers include IBM and International Computer Limited

(ICL).d) Microcomputers. These are the personal computers commonly used for office and

leisure activities. Examples include Hewlett Packard (HP), Compaq and Dell. They

include desktops, laptops and palmtops.

8. Computer Based information systems

Information systems support different types of decisions at different levels of theorganizational hierarchy.

Different types of information systems serve each of these levels.Decision Support System Provide problem-specific support for non-routine, dynamic and

often complex decisions or problems. DSS users interact directly with the information

systems, helping to model the problem interactively. DSS basically provide support fornon-routine decisions or problems and an interactive environment in which decision

makers can quickly manipulate data and models of business operations.

Office Automation Systems Office automation systems support general office work forhandling and managing documents and facilitating communication. Text and image

processing systems evolved as from word processors to desktop publishing, enabling the

creation of professional documents with graphics and special layout features.

Spreadsheets, presentation packages like PowerPoint, personal database systems and note-



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taking systems (appointment book, notepad, card file) are part of OAS. In addition OAS

include communication systems for transmitting messages and documents (e-mail) and

teleconferencing capabilities.

Artificial Intelligence Systems Artificial intelligence is a broad field of research thatfocuses on developing computer systems that simulate human behaviour, that is, systems

with human characteristics. These characteristics include, vision, reasoning, learning and

natural language processing. Examples: Expert systems, Neural Networks, Robotics.

Expert System (ES) It is an advanced DSS that provides expert advice by asking users a

sequence of questions dependent on prior answers that lead to a conclusion or

recommendation. It is made of a knowledge base (database of decision rules and

outcomes), inference engine (search algorithm), and a user interface.ES use artificial

intelligence technology. It attempts to codify and manipulate knowledge rather than

information. ES may expand the capabilities of a DSS in support of the initial phase of thedecision making process. It can assist the second (design) phase of the decision making

process by suggesting alternative scenarios for "what if" evaluation.

Knowledge Based Systems/ Knowledge Work Systems (KWS). Knowledge Work

Systems support highly skilled knowledge workers in the creation and integration of new

knowledge in the company. Computer Aided Design (CAD) systems used by product

designers not only allow them to easily make modifications without having to redraw the

entire object (just like word processors for documents), but also enable them to test the product without having to build physical prototypes.

Geographic Information Systems (GIS) Geographic information systems include digitalmapping technology used to store and manipulate data relative to locations on the earth.

An example is a marketing GIS database. A GIS is different from a Global PositioningSystem (GPS). The latter is a satellite-based system that allows accurate location

determination.

Virtual Reality Systems Virtual reality systems include 3-dimensional simulation

software, where often the user is immersed in a simulated environment using special

hardware (such as gloves, data suits or head mounted displays). Sample applications

include flight simulators, interior design or surgical training using a virtual patient.

IN SUMMARY; COMPUTER GENERATIONS:-

Classification of computers into generations is based on fundamental technology. It provides a framework for growth in the computer industry.

First generation computers

i) They were bulky in size and required a large space for installation

ii) Thousands of vacuum tubes were for processing which emitted large amounts of heat

iii) They consumed a lot of power iv) Had frequent hardware failures

v) Operating speed was slow



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vi) Commercial production was difficult and costly

vii) used machine language for programming making id difficult to program

Examples include:

ENIAC- electronic numerical integrator UNIVAC- universal automatic computer

EDVAC- electronic discrete variable automatic computer

Second generation computersA new electronic switching device called transistor was invented.

i) They were more reliable than first generation hence less prone to hardware failures

ii) It easier to program since assembly language was used for programming

iii) The memory of this computer was composed of magnetic cores.iv) They were faster, smaller, consumed less power, and emitted less power than first

generation computers.

Examples include:IBM 3070, Honeywell 400

Third generation computersThe use of integrated circuit chip(IC) was introduced. IC’s means circuits consisting of

several electronic components such as transistors, capacitors, and resisters grown on a

simple chip of silicon eliminating wired integration between components.

i) They were more powerful, reliable, less expensive, smaller, and cooler to operate than

the first generation of computers,

ii) They were easier to upgradeiii) They had faster and larger capacity secondary storage

iv) Mini computers became affordable even to small companiesv) Time sharing operating system allowed interactive usage, simultaneous use many

users and online systems.

vi) They have standardization of high level programming languages for programming

vii) They employed the use of small scale integration technologyExamples include:

IBM 360, IBM 370, PDP-8

Fourth generation computers

The average number of electronic components packed on a silicon chip doubled each

year. They employed the use of large scale integration where it is possible to integrate

more than 30,000 electronic components on a single chip.i) They were more powerful,smaller,consumed less power, emitted less heat than the 1

st,

2nd

and 3rd

generation computersii) They were more reliable and less prone to hardware failures

iii) They had faster and larger primary and secondary storage compared to 3rd

generation.

iv) Use of standard high-level programming languages allowed portability of programsv) Graphical user interface made the systems easier for users to learn how to use

vi) Personal computers even more affordable to individuals



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Fifth generation computersThis was followed by ultra large scale integration where it was possible to integrate

about one million electronic components in a single chip. This progress led to creation

of a micro-processor. A micro-processor contains all the circuits needed to performarithmetic logic and control functions/core activities of the computer on a single chip.

i) They employ the use of a large memory with a very fast access time. Hard disks usedfor secondary storage are cheaper, smaller, and larger in capacity.

ii) Floppy disks, compact disks are used as portable medium for porting programs and

data from one computer to another.iii) There is a spread of high speed computer networking which has enabled multiple

computers to be connected to enable them to communicate and share data.

iv) Companies have developed graphical user interfaces to enable individuals who are notcomputer professionals to use them by making computers more user friendly.

v) Portable computers are more smaller allowing users to use computing facility while

travelingvi) They are more powerful, consume less power, more reliable than the earlier

generations.

vii)Many types of computers , in all price ranges have come up

IN SUMMARY; CLASSIFICATION OF COMPUTER SYSTEMS:-

a) Super computers

Computers are classified according to size, processing speed, cost e.t.c they are

classified as

They are very powerful (have high processing power). They are used for processinglarge amounts of data related to a single complex problem. They are optimized for

those applications that are beyond the reach of the contemporary computers. They areused for scientific purposes, weather forecasting, space missions, nuclear research and

parallel computing. It has limited use because of the price tag. Mostly research centre’s

and government agencies with scientific/ engineering functions have them. Only a few

are operational.

b) Main frame computersIt is a large general purpose computer to which other computers can be connected to so

that they can share the facilities of the information processing facility e.g ATM’S they

are designed to be used by hundred’s of users simultaneously and handle vast amounts

of data. It has a sophisticated operating system that can run both batch and online

processing programs. It allows multi user online use, multi tasking and multiprocessing. The primary function of mainframes today is to support large databases.

They are owned by large businesses and government organisations that need a centraldepository of data that can be managed and controlled centrally.

c) Mini computersHardware components of these are often similar to those of mainframes in terms of

functionality although their features and capabilities are less powerful. Depending on

the system design, a mini computer can support a large number of terminals either

attached locally or using communication lines. It is an intermediate size computer that



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can run the same kinds of applications as mainframes but lack the speed and storage

capacity.

d) Micro computersThis is a computer whose C.P.U is a micro-processor. A micro processor is one whose

components are on a single integrated circuit chip. Hardware components are alsosimilar to those of mainframes and mini computers. However they are generally of a

smaller scale e.g portable computer, embedded computers e.g calculators, watches

Advantages of a Computer

Computer systems have many advantages, some of which are listed as follows:

1. Computers operate at high speed, hence there may be cost savings e.g. staff costs,

equipment costs etc.2. Computers produce accurate results (information).

3. Computers can work continuously without getting bored or tired.

4. Computers can work on voluminous data items.

5. Computers can work on any problem (solve any problem), provided a relevant

instruction set (program) are availed to them.

6. Computers are flexible, (i.e. they can adapt to any workload without much strain).7. Computers produce reliable information.8. Large volumes of data can be conveniently stored, assessed and altered.

9. Computers can provide useful information to management for control and decision

making.

10. Computers help to reduce paper work significant

11.Computer systems can reduce the number of persons required for performing

various organizational activities.

12.The use of computers for office activities reduces the requirements of office space



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Notes:

The above advantages may bring several benefits into the organization. Such benefits may

be classified as cost savings, improved data processing quality and better managementinformation.

1.3.4 Disadvantages of Using a Computer

As much as we say that computers are useful to humans, they come with somedisadvantages are given as follows:

a) Computers are costly, if it is more efficient and effective to carry out the

processing tasks without employing the use of computers, then computerizationis needless. Computer prices have gone down tremendously, however, but they

are still out of reach for many poor people b) Due to rapid change in the computer technology, the computer and related

facilities can become outdated very fast, hence posing a risk of capital loss.c) Changing from the old system, the manual system, to a computerized system is

a gradual process during which there is interruption in the normal working

environment.

d) There is usually the fear that installing the computer into an organization might

result in replacing some human employees.

e) In case the computer system fails, it might be extremely difficult to revert backto the old manual system. For this reason, stand by procedures are necessary,

but expensive.

f) Controlling a computer file's contents is a difficult exercise due to the fact thatthe contents of files of computer based systems are none-human sensible. There

is further fear that such contents may suffer from fraudulent acts by the peoplewho know them.

g) Manual systems, though slow, are more flexible as compared to the

computerized systems.

h) Employees may resist the adoption of computers by organizations in which they

work



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1.3.4 Resistance from Empl

It is human nature to fear theused to sometimes, there is rereasons for this resistance are:

Fear of change: Peop

Fear of losing their j

and hence they will be

Fear of failure: Sincethe people will be afra

Loss of control: Thethey might lose contro

Lack of Understand

system in their jobs.

upon as an intruder.

yees

unknown; we are always comfortable doinsistance from employees/users to adopt new

le are creatures of habit and hence are afraid

bs: People usually associate the computerafraid that they might end up losing their jo

the computer is very new in a given workinid that they might never adapt to it

management will be afraid that once a col of the organization.

ing: The user may not understand the behus this will create resistance since the co

work the way we aretechnology. The main

of change

ith loss of jobs s.

environment,

puter is implemented,

efits of the computermputer will be looked



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B: COMPUTER SYSTEMA computer is a complex system consisting of both hardware and software components.

CS=H/w+S/w+L/w

• In thinking about The Wizard of Oz , you are thinking about information, not about

something physical. You would not usually think about the actual material used to store

the information (movie film or a DVD) nor about the device which uses the information

(a movie projector or a DVD player). A DVD is physical, but the movie itself is

intangible information. When you speak of a movie, you usually mean the intangiblemovie, not a particular device that has a record of it. (Although human language is

wonderfully flexible; if you were in a video store and someone asked you to hand them

"The Wizard of Oz" you would probably hand them the correct DVD.)

• The word hardware is used for physical devices such as TV sets, DVD players and

computers. The word software is used for the information used with such devices:

movies, music, novels, computer programs, and data.

• When talking about computer systems, hardware means the physical parts of the

computer. Software means the programs and data used with the physical computer.

• Information is funny stuff. The information for the web page you are looking at isrecorded on a hard disk inside a computer located in New Britain, Connecticut. The

information was copied from physical device to physical device perhaps hundreds oftimes before it got to your computer where a program used it to display these words on

your monitor. Clearly the information is something separate from the devices used to

store and transmit it.

• A computer system consists of both hardware and software components.

• The hardware components of a computer system are the electronic and mechanical

parts. The software components of a computer system are the data and the

computer programs.

The major hardware components of a computer system are:

CPU – the brain of the computer, the CPU (central processing unit) performs all the instructionsPrimary Storage – also known as Main Memory, used by the computer to store information andinstructions while the machine is operating.

Secondary Storage –used by the computer to store information long term. Powering off a

computer does not affect data in Secondary storage. Example hard drive

Input Devices –allow users to enter data into the computer. The most common are a keyboard

and mouse

Output Devices – output devices allow computer to pass information to the user. Common onesinclude the printer and monitor.



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COMPUTER HARDWAR

These are the physical or tfunctions including; input, ou

INPUT DEVICESInput is any data or instructmemory, the CPU can access programs, commands, and us

An input device is acommands, and user responsdevices, scanners and readingdevices for physically challenTHE KEYBOARD

You enter data into akeyboards usually have from

laptops contain fewer keys.the alphabet, numbers, spaceand asterisk (*). A keyboarinstructions into the computer

Function keys are sptasks. Keyboards also containThe insertion point is a symwill display .Many of theCD/DVD drive and adjust spe

angible components of a computer syste put, storage, processing and communication.

ons you enter into the memory of a compit and process the input into output. Four tr responses:y hardware component that allows you toes into a computer. Input devices includedevices, digital cameras, audio and video i

ged users

computer by pressing the keys on the keybo101 to 105 keys, while keyboards for sma

computer keyboard includes keys that allo, punctuation marks, and other symbols sucd also contains special keys that allow.

cial keys programmed to issue commandskeys that can be used to position the insertiol that indicates where on the screen the newer keyboards include buttons that alloaker volume.

. They perform five

uter. Once input is in pes of input are data,

enter data, programs,he keyboard, pointing put devices, and input

rd. Desktop computerler computers such as

you to type letters ofas the dollar sign ($)ou to enter data and

nd accomplish certainon point on the screen.ext character you type

you to access your



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POINTING DEVICESA pointing device is an input device that allows you to control a pointer on the screen. In a

graphical user interface, a pointer is a small symbol on the display screen. A pointer often takesthe shape of a block arrow, an I-beam (T) or a pointing hand. Using a pointing device, you can

position the pointer to move or select items on the screen. For example, you can use a pointing

device to move the insertion point; select text, graphics, and other objects; and click buttons,

icons, links, and menu commands.

Common pointing devices include the mouse, trackball, touchpad, pointing stick, joystick, touch

screen, light pen, and graphics tablet.

Trackball Some users opt for alternative pointing devices other than a mouse, such as a trackball. Whereas

a mechanical mouse has a ball mechanism on the bottom, a trackball is a stationary pointing

device with a ball mechanism on its top.

Touchpad A touchpad or trackpad is a small, flat, rectangular pointing device that is sensitive to pressure

and motion. To move the pointer using a touchpad, you slide your fingertip across the surface ofthe pad. Some touchpads have one or more buttons around the edge of the pad that work likemouse buttons; on others, you tap the pad’s surface to simulate mouse operations such asclicking. Stick A pointing stick is a pressure-sensitive pointing device shaped like a pencil eraser that was firstdeveloped by IBM for its laptop computers. Because of its small size, the pointing stick is positioned between keys on the keyboard. To move the pointer using a pointing stick, you pushthe pointing stick with your finger. The pointer on the screen moves in the direction that you push the pointing stick. Joystick Users running game software such as a driving or flight simulator may prefer to use a joystick as

their pointing device. A joystick is a vertical lever mounted on a base. You move the lever indifferent directions to control the actions of a vehicle or player. The lever usually includes buttons called triggers that you can press to activate certain events. Some joysticks also haveadditional buttons that you can set to perform other actions.

Touch ScreenA monitor that has a touch-sensitive panel on the screen is called a touch screen. You interactwith the computer by touching areas of the screen with your finger, which acts as an inputdevice. Because they require a lot of arm movements, touch screens are not used to enter largeamounts of data. Instead you touch words, pictures, numbers, or locations identified on thescreen. Pen Input Many input devices use an electronic pen instead of a keyboard or mouse for input. Some of

these devices require you to point to onscreen objects with the pen; others allow you to inputdata using drawings, handwriting, and other symbols that are written with the pen on a surface. LIGHT PENA light pen is a handheld input device that contains a light source or can detect light. Some light

pens require a specially designed monitor, while others work with a standard monitor. Instead oftouching the screen with your finger to interact with the computer, you press the light pen against

the surface of the screen or point the light pen at the screen and then press a button on the pen.

Light pens are used in applications where desktop space is limited such as in the health-care field

or when a wide variety of people use the application, such as electronic voting.



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GRAPHICS TABLETA graphics tablet, also called a digitizer or digitizing tablet, consists of a flat, rectangular,

electronic plastic board used to input drawings, sketches, or other graphical data. Each locationon the graphics tablet corresponds to a specific location on the screen. When you draw on the

tablet with either an electronic pen or a puck, the tablet detects and converts the movements intodigital signals that are sent into the computer.

SCANNERS AND READING DEVICES

These devices capture data from a source document, which is the original form of the data. When

using a keyboard or pointing device to enter data, the source document might be a timecard,order blank, invoice, or any other document that contains data to be processed.

Devices that capture data directly from source documents include optical scanners, optical

character recognition devices, optical mark recognition devices, bar code scanners, and

magnetic-ink character recognition readers. Examples of source documents used with these

devices include advertisements, brochures, photographs, inventory tags

Optical Scanner

An optical scanner, usually simply called a scanner, is a light-sensing input device that reads printed text and graphics and then translates the results into a form the computer can use. The

density of the dots, known as the resolution, determines sharpness and clearness of the resulting

image. Resolution typically is measured in dots per inch (dpi), and is stated as the number of

columns and rows of dots

OPTICAL CHARACTER RECOGNITION Optical character recognition (OCR) is a technology that involves reading typewritten, computer- printed, or handwritten characters from-ordinary documents and translating the images into aform that the computer can understand. Most OCR devices include a small optical scanner forreading characters and sophisticated software for analyzing what is read.Optical Mark Recognition (OMR)

Optical mark recognition (OMR) devices read hand-drawn marks such as small circles orrectangles. A person places these marks on a form, such as test, survey, or questionnaire answer

sheet

Bar Code Scanners

A bar code scanner uses leaser beams to read bar codes (Figure 3-4). A bar code scanner is an

identification code that consists of a set of vertical lines and spaces of different widths. The bar

code, which represents some data that identifies the item, is printed on a product’s package or ona label that is affixed to a product so it can be read by a bar code scanner. The bar code scanner

uses light patterns form the bar code lines to identify the item. Magnetic Ink Character Recognition Reader A Magnetic-ink character recognition (MICR) reader is used to read text printed withmagnetized ink. MICR is used almost exclusively by the banking industry for check processing.Each check in your checkbook has precoded MICR characters on the lower-left edge; thesecharacters represent the bank number, your account number, and the check number.DIGITAL CAMERASA digital camera allows you to take pictures and store the photographed images digitally insteadof on traditional film. With some digital cameras, you download, or transfer a copy of, the stored pictures to your computer by connecting a cable between the digital camera and your computerand using special software included with the camera. With other digital cameras, the pictures arestored directly on storage media such as a floppy disk, PC Card, or flash card Audio Input Audio input is the process of entering (recording) music, speech, or sound effects. To record highquality sound, your personal computer must have a sound card. (Most new computers today



Gabriel© 19

come equipped with a sound card.) Sound is entered via a device such as a microphone, tape player, or audio CD player, each of which plugs into a port on the sound card. External MIDIdevices such as an electric piano keyboard also can connect to the sound card for audio input. Speech Recognition

Another use for a microphone is speech recognition. Speech recognition, also called voicerecognition, is the computer’s capability of distinguishing spoken words. Speech recognition programs do not understand speech; they only recognize a vocabulary of certain words. Thevocabulary of speech recognition programs can range from two words (such as Yes and No) tomore than sixty thousand words.Video Input Video input or video capture is the process of entering a full-motion recording into a computerand storing the video on a hard disk or some other medium. To capture video, you plug a videocamera, VCR, or other video device into a video capture card, which is an expansion card thatconverts the analog video signal into a digital signal that a computer can understand. (Most newcomputers are not equipped with a video capture card.) Once the video device is connected to thevideo capture card, you can begin recording. After you save the video on a hard disk, you can

play it or edit it using video-editing software.Videoconferencing A videoconference is a meeting between two or more geographically separated individuals whouse a network or the Internet to transmit audio and video data. To participate in avideoconference, you must have a microphone, speakers, and a video camera mounted on yourcomputer. As you speak, members of the meeting hear your voice on their speakers. Any imagein front of the video camera, such as a person’s face, displays in a window on each participant’sscreen.

OUTPUT DEVICES

WHAT IS OUTPUT?

Output is data that has been processed into a useful form called information. That is, acomputer processes input into output. Computers generate several types of output, depending onthe hardware and software being used and the requirements of the user. You may choose todisplay or view this output on a monitor, print it on a printer, or listen to it through speakers or aheadset. Four common types of output are text, graphics, audio, and video.An output device is any computer component capable of conveying information to a user.Commonly used output devices include display devices, printers, speakers, headsets, data projectors, facsimile machines, and multifunction devices1. PRINTERS

A printer is an output device that produces text and graphics on a physical medium such as paper or transparency film. Printed information is called hard copy because the informationexists physically and is a more permanent form of output than that presented on a display device

(soft copy).Hard copy, also called a printout, can be printed in portrait or landscape orientation.Generally, printers can be grouped into two categories: impact and no impact. Printers in each

of these categories are discussed in the following sections.i) Impact PrintersAn impact printer forms characters and graphics on a piece of paper by striking a mechanism

against an ink ribbon that physically contacts the paper. Because of the striking activity, impact printers generally are noisy. Many impact printers do not provide letter quality print.Impact printers also are ideal for printing multipart forms because they easily can print throughmany layers of paper. Finally, impact printers are used in many factories and at retail counters because they can withstand dusty environments, vibrations, and extreme temperatures.

Two commonly used types of impact printers are dot-matrix printers and line printers. Each ofthese printers is discussed in the following sections.



20 Gabriel©

Dot-matrix printersA dot-matrix printer is an impact printer that produces printed images when tiny wire pins on a

print head mechanism strike an inked ribbon. When the ribbon presses against the paper, itcreates dots that form characters and graphics. Most dot-matrix printers use continuous-form

paper, in which each sheet of paper is connected together. The pages generally have holes punched along two opposite sides so the paper can be fed through the printer Line Printer

A line printer is a high-speed impact printer that prints an entire line at a time. The speed of aline printer is measured by the number of lines per minute (1pm) it can print. Capable of printingup to 3,000 lines per minute (1pm), these printers often are used with mainframes,minicomputers, or with a network in applications such as manufacturing, distribution, orshipping. ii) Non impact Printers

A non impact printer forms characters and graphics on a piece of paper without actuallystriking the paper. Some spray ink, while others use heat and pressure to create images. Becausethese printers do not strike the paper, they are much quieter than the previously discussed impact

printers.Three commonly used types of non impact printers are ink-jet printers, laser printers, and thermal printers. Each of these printers is discussed in the following sections. Inkjet printers

An ink-jet printer is a type of non impact printer that forms characters and graphics byspraying tiny drops of liquid ink onto a piece of paper. Ink-jet printers usually use individualsheets of paper stored in a removable or stationary tray. These printers can produce letter-qualitytext and graphics in both black-and-white and color on various materials such as envelopes,labels. Laser printers

A laser printer is a high-speed, high-quality no impact printer. Laser printers for personalcomputers usually use individual sheets of paper stored in a removable tray that slides into the

printer case. Some laser printers have trays that can accommodate different sizes of paper, whileothers require separate trays for letter- and legal-sized paper. Most laser printers have a manualfeed slot where you can insert individual sheets and envelopes. You also can print transparencieson a laser printer.

Laser printers can print text and graphics in very high quality resolutions, ranging from 600dpi to 1,200 dpi. While laser printers typically cost more than ink-jet printers, they also are muchfaster, printing text at speeds of four to thirty pages per minute.Thermal printers

A thermal printer generates images by pushing electrically heated pins against heat-sensitive paper. Standard thermal printers are inexpensive, but the print quality is low and the images tendto fade over time. Thermal printers are, however, ideal for use in small devices such as addingmachines.

iii) Portable PrintersA portable printer is a small, lightweight printer that allows a mobile user to print from alaptop or handheld computer while travelling. Barely wider than the paper on which they print, portable printers easily can fit in a briefcase alongside a laptop computer.iv)Plotters and Large-Format Printers

Plotters and large-format printers are sophisticated printers used to produce high-quality

drawings such as blueprints, maps, circuit diagrams, and signs. Because blueprints, maps, andother such drawings can be quite large, these printers typically can handle paper with widths up

to 60 inches. Some plotters and large-format printers use individual sheets of paper, while otherstake large rolls. These printers are used in specialized fields such as engineering, drafting, and

graphic art and usually are very costly.



Gabriel© 21

Two basic types of plotters are pen plotters and electrostatic plotters. A pen plotter usesone or more color pen light beams, or a scribing device to draw on paper or transparencies. Pen

plotters differ from other printers in that they produce continuous lines, whereas most printersgenerate lines by printing a closely spaced series of dots.

An electrostatic plotter uses a row of charged wires (called styli) to draw an electrostatic pattern

on specially coated paper and then fuses toner to the pattern. The printed image is composed of a

series of very small dots, which provide high-quality output.

2. DISPLAY DEVICESA display device is an output device that visually conveys text, graphics, and video

information. Information shown on a display device often is called soft copy, because the

information exists electronically and is displayed for a temporary period of time.

CRT Monitors

A CRT monitor, or monitor, is a display device that consists of a screen housed in a

plastic or metal case. A color monitor displays text, graphics, and video information in color.

Monitors that display only one color are considered monochrome. A monochrome monitordisplays text, graphics, and video information in one color (usually white, amber, or green) on a

black backgroundMonochrome monitors are less expensive than color monitors. Most monitors are referred to by

their viewable size, which is the diagonal measurement of the cathode ray tube inside the

monitor and is larger than the actual viewing area provided by the monitor. LCD displays

LCD displays commonly are used in laptop computers, handheld computers, digital watches,’

and calculators because they are thinner and more lightweight than CRT monitors.

Gas Plasma Monitors

For even larger displays, some large business or power users prefer gas plasma monitors, which

can measure more than 42 inches and hang directly on a wall MONITOR QUALITY The quality of a monitor’s display depends largely on its resolution, dot pitch, and refresh rate.

The resolution, or sharpness and clarity, of a monitor is related directly to the number of pixels it

can display. Resolution is expressed as two separate numbers: the number of columns of pixels

and the number of rows of pixels a monitor can display. A monitor with a higher resolution

displays a greater number of pixels, which provides a smoother image. Another factor that determines monitor quality is dot pitch, which is a measure of imageclarity. The dot pitch is the vertical distance between each pixel on a monitor. The smaller thedistance between the pixels, the sharper the displayed image. Text created with a smaller dot pitch is easier to read. To minimize eye fatigue, you should use a monitor with a dot pitch of .28

millimeters or smaller.3. AUDIO OUTPUT (speakers, headsets)Audio is music, speech, or any other sound. Audio output devices are the components of a

computer that produce music, speech, or other sounds, such as beeps. Two commonly used audiooutput devices are speakers and headsets

To boost the low bass sounds, you can add a woofer (also called a subwoofer). The stereospeakers and woofer are connected to ports on the sound card. Most speakers have tone andvolume controls so you can adjust these settings.4. DATA PROJECTORS

A data projector takes the image that displays on a computer screen and projects it onto ascreen so that an audience of people can see the image clearly. Data projectors can be largedevices attached to a ceiling or wall in an auditorium, or they can be small portable devices Two



22 Gabriel©

types of smaller, lower-cost units are LCD projectors and DLP projectors.

LCD projector An LCD projector, which uses liquid crystal display technology, attaches directly to a

computer and uses its own light source to display the information shown on the computer screen.Because LCD projectors tend to produce lower-quality images, some users prefer to use a DLP projector for sharper, brighter images.A digital light processing (DLP) projector uses tiny mirrors to reflect light, producing crisp, bright, colorful images that remain in focus and can be seen clearly even in a well-lit room.5. FACSIMILE (FAX) MACHINE

A facsimile (fax) machine is a device that transmits and receives documents over telephonelines. The documents can contain text, drawings, or photographs, or can be handwritten. Whensent or received via a fax machine, these documents are known as faxes. A stand-alone faxmachine scans the original document, converts the image into digitized data, and transmits thedigitized image. A fax machine at the receiving end reads the incoming data, converts thedigitized data into an image, and prints or stores a copy of the original image.

Fax capability also can be added to your computer using a fax modem. A fax modem is acommunications device that allows you to send (and sometimes receive) electronic documents asfaxes. A fax modem transmits computer-prepared documents, such as a word processing letter,or documents that have been digitized with a scanner or digital camera. A fax modem is like aregular modem except that it is designed to transmit documents to a fax machine or to anotherfax modem.6. VIDEO CARDS

To display color, a color monitor works in combination with a video card, which is includedwith today’s personal computers. A video card, also called a graphics card or video adapter,converts digital output into an analog video signal that is sent through a cable to the monitor. Themonitor separates the video signal into red, green, and blue signals. Electron guns then fire thethree color signals to the front of the monitor. These three dots - one red, one green, and one blue

are combined to make up each single pixel.The number of colors that a video card can display is determined by the number of bits it

uses to store information about each pixel



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THE COMPONENTS IN THE SYSTEM UNIT

1. Central Processing Unit (CPU)

The system unit is a box-like case housing the electronic components of a computer that areused to process data. System unit components include the processor, memory module,expansion cards, and ports and connectors. Many components reside on a circuit board calledthe motherboard or system board. The motherboard contains different types of chips, or small

pieces of semi conducting material on which one or more integrated circuits (IC) are etched.One of the more important chips is the central processing unit.

2. The System UnitThe system unit, sometimes referred to as the processor, interprets and carries out the basic

instructions that operate a computer. That is, most of the devices connected to the computercommunicate with the CPU in order to carry out a task. The CPU contains the control unit andthe arithmetic/logic unit.

The Control Unit The control unit, one component of the CPU, directs and coordinates most of the operations

in the computer. For every instruction, the control unit repeats a set of four basic operationscalled the machine cycle (1) fetching the instruction or data item from memory, (2) decodingthe instruction into commands the computer understands, (3) executing the commands, and, if

necessary, (4) storing, or writing, the result to memory. Arithmetic/Logic unit

The arithmetic/logic unit, another component of the CPU, performs the arithmetic,comparison, and logical operations. Arithmetic operations include addition, subtraction,multiplication, and division. Comparison operations involve comparing one data item to anotherto determine if the first item is greater than, equal to, or less than the other item. Logicaloperations work with conditions and logical operators such as AND, OR, and NOT

RegistersThe CPU uses temporary storage locations called registers, to hold data and instructions. The

function include storing location of where instruction was fetched storing an instruction while itis being decoded, storing data while the ALU processes it, and storing the results of acalculation.

Arithmetic Logic Unit (ALU) CONTROL UNIT (CU)

Performs basic arithmetic calculations selects and interprets program insAnd logical comparisons tructions and then sees that they

are executed

REGISTERS

Used to hold information on a temporary basis

MAIN MEMORY

RAM and ROM

SECONDARY STORAGE DEVICES

Floppy disk

Compact disk

Hard disk



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4. MemoryIn the system unit, a computer’s memory stores data, instructions, and information. Memory

stores three basic items: The operating system and other system software that control the usageof the computer equipment; Application programs designed to carry out a specific task such as

word processing; and The data being processed by application programs. RAM

RAM (random access memory) is a memory chip that the processor can read from and writeto. RAM is volatile memory, meaning that its contents are lost when the computer’s power isturned off. Multiple programs can be loaded into RAM simultaneously, provided you haveenough RAM to accommodate all the programs. The program with which you are workingcurrently displays on the screen. Basic types of RAM include dynamic RAM and static RAM,RDRAM (Rambus DRAM), Synchronous DRAM (SDRAM)

ROM ROM (read-only memory) is a memory chip that only can be read and used; that is, it cannot

be modified. ROM is non-volatile memory, meaning that its contents are not lost when thecomputer’s power is turned off.

Commonly used for storing of program instructions that are not subjected to change. Generally provided by manufacturer. ROM chips that contain permanently written data, instruction, orinformation are called firmware. Another type of ROM chip, called programmable read onlymemory (PROM) clip, is a blank ROM chip on which you can permanently place items. Theinstructions used to program a PROM chip are called micro-code. Once the micro-code is programmed into the PROM chip, it functions like a regular ROM chip and cannot be erased orchanged.

Flash memoryAnother type of non-volatile memory is called flash memory or flash ROM. Unlike a PROM

clip that can be programmed only once, flash memory can be erased electronically andreprogrammed. Flash memory is used to store programs on personal computers, as well ascellular telephones, printers, digital cameras, pagers, and personal digital assistant. Flash

memory is available in sizes ranging from 1 to 40 MB.CMOS

Another of memory clip in the memory unit is complementary metal-oxide semiconductor(CMOS). CMOS memory is non-volatile memory used to store configuration information aboutthe computer, such as the type of disk drives, keyboard, and monitor; the current date and time;and other start-up information needed when the computer is turned off. CMOS use battery power to retain information even when the power to the computer is turn off. Battery-backedCMOS memory thus keeps the calendar, date, and time current even when the computer poweris off. Unlike ROM, information stored in CMOS memory can be changed, such as when youchange from standard time to daylight saving time

Expansion Slots and Expansion BoardsAn expansion slot is an opening, or socket, where a circuit board can be inserted into the

motherboard. These circuit boards, sometimes referred to as expansion boards or expansioncards, add new devices or capabilities to the computer, such as a modem or more memory. Plugand Play refers to a computer’s capability to automatically configure expansion boards andother devices as they are installed.

Port A cable often attaches external devices to the system unit. The interface or point of

attachment, to the system unit is called a port. Ports have different types of connectors used to join a cable to a device.i)Serial Port

A serial port is one types of interface used to connect a devices to the system unit. Because aserial port transmits only one bit of data at a time, it usually is used to connect devices that donot require fast data transmission rates, such as a mouse, keyboard, or modem



Gabriel© 25

ii) Parallel Port Unlike serial port, a parallel port is an interface used to connect devices that are capable of

transferring more than one bit at a time. Parallel ports originally were developed as analternative to the slower speed serial ports.

Many printers connect to the system unit using a parallel port with a 25-pin female connector.This parallel port can transfer eight bits of data simultaneously through eight separate lines in a

single cable

Types of Processors

CISC Processors (Complex instruction set computing)

One of the earlier goals of CPU designers was to provide more and more instructions in the

instruction set of the CPU, to ensure it directly supports more features making it easier totranslate high level language programs to machine language and to ensure machine language

programs run more effectively. However every additional instruction in the instructions set of theCPU requires the necessary hardware circuitry to handle such instructions, adding more

complexity to CPU’s hardware circuitry.

Another goal of CPU designers was to optimize the usage of expensive memory, to

achieve this they tried to pack more instructions in the memory by introducing the concept of

variable length instructions. CISC processors possess many processing features whereby makingthe job of machine programmers easier. They are complex and expensive to produce.

RISC Processors (Reduced instruction set computing)

In early 1980 some CPU designers discovered that several of the instructions supported by CISC

CPU’s are rarely used hence came out with an idea that the complexity of the CPU design can be

greatly reduced by implementing only a bare minimum basic set of instructions plus some of themore frequently used instructions in the hardware circuitry of the CPU. Other complex

instruction did not need to be supported in the instruction set in the CPU because they canalways be implemented in software by using the basic set of instructions.

The designers came up with the idea of making all instructions of uniform length so thatthe decoding and execution of all instructions becomes simple and fast. This design resulted in

producing a faster and less expensive processor. They have a small instruction set thereby placing extra demand on programmers who must consider how to implement complex

computations by combining simple instructions. Due to a simple design RISC processors are

faster for most applications, less complex and less expensive to produce than CISC processors.

MEMORY (STORAGE DEVICES)While performing a processing operation, the CPU needs a place to temporarily holdinstructions to be executed and data to be used with those instructions. Memory, which iscomposed of one or more chips on the motherboard, holds data and instructions while they are being processed by the CPU.

The two basic types of memory are volatile and non-volatile. The contents of volatilememory, such as RAM, are lost (erased) when the power to the computer is turned off. Thecontents of non-volatile memory, however, are not lost when power is removed from thecomputer. For example, once instructions have been recorded onto a non-volatile ROM chip,they usually cannot be erased or changed, and the contents of the chip are not erased when power is turned off.



26 Gabriel©

SECONDARY STORAGEStorage, also called secondary storage, auxiliary storage, or mass storage, holds items such as

data, instructions, and information for future use. Think of storage a filing cabinet used to holdfile folders, and memory as the top of your desk. When you need to work with a file, you

remove it from the filing cabinet (storage) and place it on your desk (memory). When you arefinished with the file, you return it to the filing cabinet (storage).Storage is non-volatile, which means that items in storage are retained even when power is

removed from the computer. A storage medium (media is the plural) is the physical material onwhich items are kept. One commonly used storage medium is a disk, which is a round, flat pieceof plastic or metal with a magnetic coating on which items can be written. A storage device isthe mechanism used to record and retrieve items to and from a storage medium.The speed of a storage device is defined by its access time, which is the minimum time it takes

the device to locate a single item on a disk. Compared to memory, storage devices are slow.The size, or capacity, of a storage device, is measured by the number of bytes (characters)

1. FLOPPY DISKSA floppy disk, or diskette, is a portable, inexpensive storage medium that consists of a thin,

circular, flexible plastic disk with a magnetic coating enclosed in a square-shaped plastic shell.When discussing a storage medium, the term portable means you can remove the medium fromone computer and carry it to another computer. A floppy disk drive is a device that can readfrom and write to a floppy disk.

2. HARD DISKSWhen personal computers were introduced, software programs and their related files required

small amounts of storage and fit easily on floppy disks. As software became more complex andincluded graphical user interfaces and multimedia, file sizes and storage requirements increased.Today, hard disks - which provide far larger storage capacities and much faster access timesthan floppy disks - are one of the primary media for storing software programs and files.Current personal computer hard disks can store from 4 GB and above of data, instructions, andinformation.

A hard disk usually consists of several inflexible, circular disks, called platters, on which itemsare stored electronically. 3. COMPACT DISCSA compact disc (CD) is a flat, round, portable, metal storage medium that usually is 4.75

inches in diameter and less than one-twentieth of an inch thick (Figure 5-8). Compact disksstore items such as data, instructions, and information by using microscopic pits (indentations)and land (flat areas) that are in the middle layer of the disc.CD-ROMsCD-ROM (pronounced SEE-DEE-Rom, is an abbreviation for compact disc read-only

memory) The contents of standard CD-ROMs are written, or recorded, by the manufacturer andonly can be read and used. That is, they cannot be erased or modified- hence, the name read-only. A CD-ROM can hold up to 700 MB of data, instructions, and information, or about 450

times that which can be stored on a high-density 3.5-inch floppy disk.CD-R (compact disc-recordable)Is a technology that allows you to write on a compact disc only once using your own

computers? Once you have recorded the CD-R, you can read from it as many times as you wish.CD-RW (compact disc-rewriteable)Is an erasable disc that you can write on multiple times CD-RW overcomes one of the

disadvantages of CD-R disks - that you can write on them only once. DVD-ROMsA DVD-ROM (digital video disc-ROM) is an extremely high capacity compact disc capable of

storing from 4.7 GB to 17 GB - more than enough to hold a telephone book containing everyresident in the United States. Not only is the storage capacity of a DVD-ROM greater than aCD-ROM, a DVD-ROM’s quality also far surpasses that of a CD-ROM.



Gabriel© 27

4. MAGNETIC TAPES One of the first storage media used with mainframe computers was magnetic tape, a

magnetically coated ribbon of plastic capable of storing large amounts of data and informationat a low cost. Tape storage requires sequential access, which refers to reading or writing data

consecutively. Like a music tape, you must forward or rewind the tape to a specific point toaccess a specific piece of data. 5. PC CARDS

A PC Card is a thin, credit card-sized device that fits into a PC Card expansion slot on a

laptop or other personal computer. Different types and sizes of PC Cards are used to addstorage, additional memory, communications, and sound capabilities to a computer.

6. Picture card or compact flash cardSome digital cameras also use a matchbook-size card, sometimes called a picture card or

compact flash card, to store pictures, which are then transferred to a computer by inserting thecard into a card reader or slot. These compact flash cards have storage capacities ranging from2 MB to 256 MB.

7. Smart Cards

A smart card, which is similar in size to a credit card or ATM card, stores data on a thinmicroprocessor embedded in the card. An intelligent smart card contains a CPU and has input,

process, output, and storage capabilities. In contrast, a memory card has only storage

capabilities. When the smart card is inserted into a specialized card reader, the information onthe smart card is read and, if necessary, updated.

8. Microfilm and Microfiche

Microfilm and microfiche are used to store microscopic images of documents on roll orsheet film. Microfiche uses a small sheet of film, usually about four inches by six inches. Theimages are recorded onto the film using a device called a computer output microfilm (COM)recorder. The stored images are so small they can be read only with a microfilm or microfichereader.

Applications of microfilm and microfiche are widespread. Libraries use these media to store back issues of newspapers, magazines, and genealogy records. Large organizations usemicrofilm and microfiche to archive inactive files. Banks, for example, use it to storetransactions and cancelled checks, and the U.S. Army uses it to store personnel records. Usingmicrofilm and microfiche provides a number of advantages: it greatly reduces the amount of paper firms must handle; it is inexpensive; and it has the longest life of any storage medium.



28 Gabriel©

Relationship among the hardware, system software, application software and users of a

computer system

C:COMPUTER SOFTWARE

Software is a set of computer programs, procedures and associated documents which describe

the programs and how they are to be used. A computer program is a sequence of logical

instructions, written in a language, which can be understood by the computer which controls the

activity of processing by the computer.

Most software can be divided into two major categories System software

Application software

Application software

A set of one or more programs, designed to solve a specific problem or do a specific task. E.g. Word processing – enables us to make use of a computer system for editing, viewing,

formatting, storing, retrieving, and printing documents e.g. Microsoft word, word perfect,

word pro, WordStar.

Spreadsheet software – a numeric data analysis tool, which allows us to create a kind of

computerized ledger e.g. Microsoft excel, lotus 1-2-3

Database software – a set of one or more programs, which enable us to create a database,maintain it, organize its data in desired fashion and to selectively retrieve useful informationfrom it. Microsoft access, Quattro pro, VISIC ALC

Graphics software – enables us to use a computer system for creating, editing, viewing,

storing, retrieving and printing designs, drawings, pictures, graphs and anything else that can

be draw in the traditional manner. Education software – allows a computer system to be used as a teaching and learning tool. Entertainment software – allows a computer system to be used as an entertainment

System software

USERS( Normally interact with the system via the user

Interface rovided b the a lication software

APPLICATION SOFTWARE

(Software that do a specific task or solve a specific problem)

SYSTEM SOFTWARE(Software that constitute the operating and programming

Environment of the computer system)

HARDWARE(Physical devices/ components of the

com uter s stem



Gabriel© 29

System software is a set of one or more programs, designed to control the operation and extendthe processing capability of a computer system. In general it performs the following functions: Supports the development of other application software Supports the execution of other application software

Monitors the effective use of various hardware resources e.g. CPU, memory, peripheral

Communicates with and controls the operation of peripheral devices e.g. printers, hard disk

Some of the most commonly known types of system software are: Operating systems – it takes care of the effective and efficient utilization of all the

hardware and software components of the computer system e.g. Microsoft DOS,

Windows, UNIX, LINUX

Programming language translators – they transform the instructions prepared by

programmers in a programming language into a form which can be interpreted and

executed by a computer system e.g. Assemblers, Compilers, Interpreters

Communication software – they enable transfer of data and programs from one

computer system to another in a network environment

Utility programs – a set of programs which help user in system maintenance tasks and in

performing tasks of routine nature. E.g. formatting hard disks

Operating System

It’s an integrated set of programs that controls the resources (CPU, Memory, Input/output

devices) of a computer system and provides its users with an interface or virtual machine that ismore convenient to use than the bear machine.

The two primary objectives of Operating System use.

(i) Making a computer system convenient to use i.e. hides details of Hardware resources

from the programmer and provides him with a convenient interface of using computer

system. It acts as an intermediary between hardware and software providing a high

level interface to low level hardware and making it easier for the software to access theuse of those resources.

(ii) Managing computer resources. This involves performing such tasks as keeping track of

who is using which resource, granting resource requests, accounting for resource

usage, and mediating conflicting requests from different programs and users.

Main functions of Operating System.(i) Process Management(ii) Memory Management

(iii) File Management

(iv) Security

(v) Command Interpretation.

Operating System arose historically as people needed to solve problems associated with usingcomputers. Much of operating system history is driven by relative cost factors of hardware and



30 Gabriel©

people. Hardware started out fantastically expensive, relative to people and the relative costs has been decreasing ever since.

(i) Process Management

A process (job) is a program in execution. The main objective of the process management

module of operating system is to manage the process submission to the system in a manner to

minimize the idle time of various processors (CPU, I/O processors e.t.c) of the computer system.

It takes care of creation and deletion of processes, scheduling of various system resources to

different processes requesting them and providing mechanisms for synchronization andcommunication among processes

Multiprogramming: This is the interleaved execution of two or more different and independent

programs by same computer. Two or more user programs are placed in the main memory and

executed consecutively.

Note: The CPU is capable of conducting / executing only one instruction at a time.

Requirements of Multi-programming System(a) Large Memory – Required to accommodate a good number of user programs along with the

operating system.(b) Memory Protection- To prevent a job in one memory partition from changing information or

instructions of a job in another memory partition.

(c) Job status preservation- preserves the job’s complete status information when the CPU istaken away from it and restores this information back, before the CPU is given back to it

again.

(d) Proper job mix - to effectively overlap the operations of the CPU and Input/output

devices.

(e) CPU scheduling – To decide which of the ready jobs should be allocated the CPU for

execution.Multitasking: Technically speaking it is the same as multiprogramming. It is system’s capability

to concurrently work on more than one task/process. Some authors prefer using

multiprogramming for multi-user systems and multitasking for single-user systems. The progress

of different tasks can be viewed on different windows in a multitasking system.

Multiprocessing: Used to describe interconnected computer configurations or computers with

two or more CPUs which have the ability to simultaneously execute several programs. Multiprocessing systems have better performance and reliability.

Note:These systems however require a very sophisticated operating system to schedule, balance and

coordinate input, output and processing activities of multiple processors. The design of such

operating system is a complex and time taking job. They are expensive to procure and maintain.(ii) Memory ManagementIts job is to keep tracks of which parts of memory are in use and which are not in use, to allocate

memory to processes when they need it and de allocate when they are done.

Virtual Memory – Extension of memory which allows execution of processes that might not be

completely loaded in memory. It is often described as hierarchy of two storage systems-one is a

low cost, large capacity, low speed system (hard disk) the other is a high cost, small capacity

high speed system (RAM). The operating system manages the two storage systems in such as away that the users of the system feel that they have access to a single, large, directly addressable

and fast main memory.



Gabriel© 31

(iii) File ManagementA file is a collection of related information. Every file has a name, data and attributes. The name

of a file uniquely identifies it in the system and is used by its users to access it. The filemanagement module of an operating system takes care of file related activities such as accessing,

naming, sharing and protection files.

File Access Methods

To use information stored in a file, it must be accessed and read into computer memory. The two

commonly supported file access methods at operating system level are:

1. Sequential Access.2. Random Access.

1.Sequential Access. A process can read the bytes or records in the file in the order in which

they are stored, starting at the beginning. A sequential file can however be rewound and read as

often as needed.

2.Random Access. Information stored in a random access file can be accessed randomly,

irrespective of the order in which the bytes or records are stored.

File Operation

An operating system provides a set of operations to deal with files and their contents. A typical

set of file operations provided by an operating system may be as follows;1. Create-Is used to create a new file.

2. Delete- Is used to delete an existing file, which is no longer needed.

3. Open-Is used to open an existing file, when a user wants to start using it.

4. Close-Is used a close a file, when a user has finished using it.

5. Read-Is used to read data stored in a file.

6. Write-Is used to write new data in a file.7. Seek-. Is used with random access file to first position the read/ write pointer to a specific

place in the file, so that data can be read from, or written to, that position.

8. Get attributes- Is used to access the attributes of a file.

(iv) Security Management

Security in a computer system deals with protecting the various resources and information ofa computer system against destruction and unauthorized access.

A total approach to computer security involves both external and internal security;

External security deals with securing the computer system against external factors such asfires, floods, earthquakes, stolen disks, leaking out of stored information by a person who has

access to the information.For external security, the commonly used methods include; maintaining adequate backup copies

of stored information at places far away from the original, information using security guards to

allow entry of only authorized persons into the computer centre. Allowing access to sensitiveinformation to only trusted users etc.

Internal security deals with:(a) User Authorization – Once a user is allowed physical access to the computing facility, the

users identification must be checked by the system before he/she can actually use the facility.

E.g. Voice recognition systems, Finger prints, Eye scanning, ATMs.



32 Gabriel©

(b) Access Control – Even when a user passes the authorization stage and is allowed to use thecomputing facility, a way is needed to prohibit the user from accessing the system’s

resources/information that he or she is not authorized to access e.g. pin number, password.(c) Cryptography – Even if a user manages to gain access to the information which he/she is

not authorized to access, a way is need to ensure that the user cannot make use of that

information. Cryptography works on the idea that if it is not possible to ensure access control,

it is better to prevent comprehension of information.

(v) Command InterpretationThe command interpretation module of an operating system provides a set of commands using

which the user can give instructions to the computer for getting some job done by it. When a

user gives instructions to the computer, the interpreter takes care of interpreting the command

and directing the system resources to handle the request hence the command interpreter

provides a user interface to hide the hardware details of the system from the user. The two

broad categories of user interface supported by various operating systems are;

(i) Command Line Interface(ii) Graphical user interface(GUI)

(a) Command Line interface: This is a textual user interface in which the user gives

instructions to a computer by typing commands. To enter a command, the user uses the

keyboard to key in words and symbols e.g UNIX and DOS.(b) Graphical user interface (GUI); It is much easier to learn and use than command line

interface. A GUI provides the screen full of graphical icons and menus and allows the user to

make a rapid selection from the displayed icons or menus to use instructions to the computer.

A point and-draw device is normally used to rapidly point to and select a particular graphical

icon or menu item from the multiple options displayed on the screen. E.g. Window, LINUX

Popular Operating Systems.1. UNIX.

It is a multi- user, timesharing operating system. It was developed in the early 1970s at the

Bell labs by Ken Thompson and Dennis Ritchie for a small PDP- 11 computer. It was the first

operating system to be written in a high level language (C – Language) since UNIX was

written in C- language moving it to a new machine was much easier. This was an importantreason for its large popularity and availability on a wide variety of systems. It has multi-

processing capability but is also used in single – processor computers. Additionally, it has a

command driven interface. It has been the most widely used multi-user network Operating

System. There are many versions that can run on many different designs of computer i.e.

mainframe computers, micro and minicomputers.2. DOS

Stands for “Disk Operating System”. It is a single user operating and IBM compatible Pcs. It

was introduced in 1981 by Microsoft and IBM and was the most popular Operating System for

personal computers in the 1980s. Its popularity stared reducing in the 1990s with the launch of

Ms Window Operating System. It is a single user operating single tasking and command

operating system.

3. Microsoft Windows:



Gabriel© 33

Developed by Microsoft to overcome the limitation of its own Dos operating system wasinitially developed as a graphical user interface for Dos not as an operating system. The first

success version of this operating System was Windows 3.00 released in1990. Other versionswere Windows 95, 98, 2000, XP, Millennium, NT, and Vista.

Windows is a single- user- multitasking operating system. Progress is represented by icons

which provide the user with ease of manipulating of file and programs i.e. clicking, double –

clicking, drag, drop, etc.

4. LINUXAn open –source operating system enhanced and backed by thousands of programmers

worldwide. Its multitasking operating systems which was originally designed for Pcs.

The Linux is derived from its inventor called Linus Torvalds. He was a student at the

University of Helsinki, Finland in the early 1990s when he wrote the first version of Linux as a

toy project. He later posted the code on the internet and asked programmers to help him build it

into a working system. The result was Linux. Torvalds holds the copyright but permits free

distribution of the source code. He oversees the development of the Kernel and its owntrademark. When someone submits a change or a feature, torvalds and his core team of kernel

developers review the merit of adding it to the source code

Ways of acquiring computer software

An organization can develop proprietary software that is unique, customized programs for aspecific application area and on the other hand a company can purchase and use an existing

software package (off-the –shelf software).

Customized/proprietary software

Programmers determine the type of software to be developed according to users specific

problems/ needs. The software can be developed by an in-house development team or by acontracted software company but based on the specific user needs.

Advantagesi) You can get exactly what you need in terms of reports, features e.t.c

ii) Being involved in development offers a further level in control over results

iii) There’s more flexibility in making modifications that may be required due to changes in

technology or environment.iv) You don’t pay for features which you won’t use

v) The user get in-house’s a competitive advantage

Disadvantages

i) The cost of developing the software is high/expensive

ii) It takes more time to developiii) It is vulnerable or prone to errors because it has not been thoroughly tested

Off –the –shelf softwareThey are readily available across the shops or from software vendors.

Advantages

i) They are cheap because development and maintenance costs are shared among many

customersii) They take less time to develop

iii) A user can start using the software almost immediately he purchases it



34 Gabriel©

iv) Possibility of errors is low because it has been properly tested

Disadvantagesi) The user pays for features he/ she may never use

ii) It does not solve all user problems

iii) It is difficult to make alterations and modifications

iv) A user may be locked/forced to using the products of a particular supplier/manufacturer

especially upgrades

D: COMPUTER NETWORKING AND DATA COMMUNICATIONS

When referring to computers, communications describes a process in which one computer

transfers data, instructions, and information to another computer(s). Communications requires: a

device that initiates the transfer (a sending device); a communications device (such as a modem)that converts the sent material into signals capable of being carried by a communications

channel; a communications channel over which the signals are sent; a communications devicethat receives the signals and converts them into a form understood by the receiving device; and a

device that accepts the sent material (a receiving device).

COMMUNICATIONS CHANNELS

An important aspect of communications is the channel, which is the communications path between two devices. A communications channel is composed of one or more transmissionmedia. Transmission media consists of materials or techniques capable of carrying one or moresignals.

TRANSMISSION MEDIATransmission media are one of two types: physical or wireless. Physical transmission

media use wire, cable, and other tangible (touchable) materials tosend communications signals; wireless transmission media send communications signals throughthe air or space using radio, Microwave, and infrared signals.1.Physical transmission media used in communications include twisted-pair cable, coaxial

cable, and fibre-optic cable. These cables typically are used within buildings or underground.2.wireless transmission media

Wireless transmission media used in communications include broadcast radio, cellular radio,microwaves, communications satellites, and infrared. Wireless transmission media are usedwhen it is impractical or impossible to install cables. Many wireless devices that access theInternet now use the WAP (Wireless Application protocol), which is a standard set of

communications specifications that help to ensure successful communications.

TRANSMISSION CHARACTERISTICSAny transmissions sent during communications can be categorized by a number of characteristics

including the signal type, transmission mode, transmission direction, and transmission rate.

Signal Type: Analog or Digital Depending on the devices and media involved, that signal is either analog or digital. Telephoneequipment originally was designed to carry only voice transmission in the form of an analogsignal, which consists of a continuous electrical wave. Computers, however, process data asdigital signals, which are individual electrical pulses that represent the bits grouped together into bytes. For telephone lines to carry digital signals, a special piece of equipment called a modemconverts between. Digital signals (0s and Is) and analog signals.



Categories of channels

Broadband vs. BasebandYou have learned that sever physical (twisted-pair cable,cellular radio, microwave, sasignal at a time, called bassimultaneously, called brotransmit signals it a much fasexample of a media that use broadband transmission are di

Transmission Direction: SimThe direction in which datasimplex, half-duplex, or full-

Simplex transmission

Data flows only in one diretransmission is used only whedevice. Security systems antransmission.

Half-duplex transmisIn half-duplex transmission, but only in one direction attransmission; you can talkmachines, credit card verifictransmission.

Full-duplex transmisIn full-duplex transmission,telephone line, for example,

the same time. Full-duplexrequirements or those with he

Transfer RatesThe speed with which a trausually is expressed as bits pin one second. Today's trans per second (Mbps) to billions

Communications softwareFor two computers to commucommunications devices are

al different types if communications medicoaxial cable, fibre-optic cable) and wirellite, infrared). Some types of these mediae-band transmission, while others can trad-band transmission. Media that use brter speed than those that use baseband transs broadband transmission. Two other widegital subscriber lines (DSL) and cable televi

lex, Half-Duplex, and Full-Duplex lows along transmission media is classified

uplex (Figure 6-7).

tion - from the sending device to the recen the sending device does not require a respd fire alarms that contain a sensor, for

ionata can flow in either direction - from sendea time. Citizens band (CB) radio, for exar listen, but you cannot do both at thetion systems, and automatic teller machine

ion data can flow in both directions at theupports full-duplex transmission, meaning

rans- mission is used for applications witavy traffic.

smission medium carries data is its transr second (bps) - that is, the number of bitsission media transmit data at rates rangin

of bits per second (Gbps).

icate, they must have compatible communi pre- programmed to accomplish commu

abriel© 35

exist, including bothless (broadcast radio,can transmit only onesmit multiple signals

oadband transmissionission. Satellite is an

spread applications ofion networks.

in one of three types:

iving device. Simplexnse from the receivingxample, use simplex

to receiver and back - ple, uses half-duplex

same time. Many faxs also use half-duplex

ame time. A regularoth parties can talk at

intensive computing

fer rate. Transfer ratehat can be transmittedfrom millions of bits

ations software. Someications tasks. Other



36 Gabriel©

communications devices require a separate communications software program to ensure propertransmission of data.

Communications software helps you establish a connection to another computer and

manage the transmission of data between computers; it resides in the main memory of the

sending and receiving computers while the connection is established.To help you establish a connection to another computer, communications software uses

wizards, dialog boxes, and other onscreen messages to prompt you for information and automate

tasks where possible. Communications software usually includes one or more of the following

features: dialing, file transfer, terminal emulation, and Internet access.The Internet access feature allows you to use the computer to connect to the Internet to

send entail, participate in chat rooms, visit World Wide Web sites, and so on. When you purchase a modem, it usually includes a basic communications software package so you canconnect to other computers, such as ones used for a bulletin board system. When you subscribeto an online service or Internet service provider, the provider typically sends you a separatecommunications software package, which you must use to connect to their computers so you can

access the Internet, send e-mail, and use their other services.Communications devicesA communications device is any type of hardware capable of transmitting data, instructions, andinformation between a sending device (sender) and a receiving device (receiver). At the sendingend, a communications device converts the data, instructions, or information from the sender intosignals understood by the transmission media on the communications channel. At the receivingend, the communications device receives the signals from the communications channel andconverts the signals into a form understood by the receiver.

Recall that sending and receiving devices include a variety of types of hardware such ashandheld computers, laptop computers, desktop computers, minicomputers, mainframes, digitalcameras, and fax machines. The type of communications device used in a communicationssystem depends on the type of sending and/or receiving devices, as well as the type of

transmission media.Some of the more common types of communications devices are modems, cablemodems, multiplexers, and network interface cards.

Today, thousands of computer networks exist, ranging from small networks operated byhome users to global networks operated by numerous telecommunications firms. To interconnect

the many types of networks that exist, various types of communications devices are used,including hubs, repeaters, bridges, gateways, and routers.

NETWORKSA network is a collection of computers and devices connected by communications channels thatallows users to share data, information, hardware, and software with other users. Individuals andorganizations connect computers in a network for a variety of reasons, including the ability toshare hardware, data and information, and software; and to facilitate communications. Networksreduce costs and increase efficiency and allowing sharing of programs, data and peripheraldevices.

Local Area Network (LAN)A local area network (LAN) is a network that connects computers in a limited geographical area,

such as a school computer laboratory, office, or group of buildings. Two popular types of LANsare peer-to-peer networks and client/server networks.A LAN is made of two or more computers

connected to each other within the same geographical area but not necessarily within the same

building.



Gabriel© 37

Metropolitan Area Network (MAN)

A MAN is a network of computers spread over a metropolitan area such as a city and its suburbs.This city bridges its LANs with a series of backbones, making one large network for the entire

city. The MAN may be operated by one organisation or be shared resources used by several

organisations in the same city.

Wide Area Network (WAN)

A wide area network (WAN) is a network that covers a large geographical area (such as a city orcountry) using a communications channel that combines telephone lines, microwave, satellites,

or other transmission media.

Network Topologies

The configuration, or physical arrangement, of the device in a communications network is called

network topology or network architecture. Three commonly used network topologies are bus,

ring, and star. Network also combinations of these topologies.

Bus Network

A node must be intelligent enough to listen to the bus and recognise own addresses in order to

receive incoming data

Ring Network Intelligent central controller. Each node has an equal amount of intelligence

Star Network

All nodes are joined at a single central point using one link for each node. Has central node,

employs switching techniques to interconnect the outlying stations. Affects the functionality ofnetwork if central host is not operating

Disadvantages of networks Networks are expensive to set up

Security problems

PROTOCOLS

A protocol is a set of rules and procedures for exchanging information among computers. Usingthe same protocols, different types and makes of computers can communicate with each other.

Ethernet

Ethernet is a LAN protocol that allows personal computers to contend for access to a network.

Token Ring

A token ring protocol controls access to a network by requiring that a special signal called a

token is shared or passed among network devices.TCP/IP TCP/IP (Transmission control protocol/Internet protocol) is a set of protocols used to manage

data transmission by breaking it up into packets.

File transfer protocol (FTP)

A set of rules used to govern the sending and receiving of files on the internet.

Telnet One of the ways that a person can access a remote computer over a network such as the internet.

It’s often used by network administrators to remotely control and/or troubleshoot the operation

of a web server. Telnet programs act as if your computer is a terminal that is connected to the

remote computer.



38 Gabriel©

IntranetsIntranets are internal networks that use Internet and Web technologies. Intranets make company

information accessible to employees and facilitate working in groups.

Extranet An extranet is an intranet that extends to authorized users outside the company. Extranets

facilitate communications among a company’s customers or suppliers.

Videoconferencing involves using video and computer technology to conduct a meeting

between participants at two or more geographically separate locations.

INTERNET

The word internet is derived from two words: interconnection and networks. The Internet,

a worldwide collection of networks, offers the World Wide Web and such popular Web-based

activities as e-commerce and Internet telephony. The internet, the world’s biggest network, is

actually a collection of smaller networks located all over the world. It can be used for a variety of purposes, such as checking e-mail, chatting, downloading files searching for information,

listening to music e.t.c in order to gain access to the vast resources found on the internet youmust first become part of one of the networks which it comprises. The networks of large

companies and universities are directly connected to the internet, so if you are part of one of

these networks and you have appropriate network privileges, you can access the internet.The average person however, gains access through a local internet service provider (ISP).

An ISP is a company with a direct connection to the internet that grants subscribers access to the

various internet services.

World Wide WebIt is basically a collection of text and multimedia documents called web pages, some of which

are linked. A web page is an electronic document written in a computer language called HTML.Web pages are usually encoded in a special language called hypertext Mark-up language

(HTML) that allows one web page to provide links to several others. A group of related web

pages on the same web server is known as a website. Each web page and website has an address

called a uniform resource locator (URL). Web pages are viewed using special software called

web browsers e.g. internet explorer, Netscape or opera. The transmission of web pages is

governed by a protocol known as Hypertext transfer protocol (HTTP).

E-mail

E-mail (electronic mail) is the exchange of text messages and computer files via acommunications network. Each person using e-mail must have an e-mail address. The e-mail

service provider has a special server to handle the e-mail for its customers. E-mails are mainly

text messages that may (Not always) have a little formatting similar to a word processingdocument. It may be used to send files attached to the e-mail message called attachments.Before mail is read, it is downloaded from the mail server to the user’s computer.

Advantages1) It is faster than normal mail.

2) It is cheaper and more convenient .e-mails are free.

3) It’s very easy to send files.

4) The same message can be easily and quickly sent to several people.



Gabriel© 39

Disadvantages1) It cannot be used to send parcels

2) You cannot send e-mail to people who do not have an e-mail account.3) E-mail makes it easy for computer viruses to be spread.

E: COMPUTER PROGRAMMING LANGUAGES

1St

Generation Programming Languages (Machine Language)the machine language of a computer is written as strings of binary (ones and zeros).the circuitry

of a computer is wired in a manner that it immediately recognizes the machine language

instructions and converts them in the electrical signals needed to execute them.

Advantages

1. Programs written in machine language can be executed very fast 2. The program can directly address and control the internal circuitry of the computer making

it more effective in hardware usage and control

Disadvantages

1. it is machine dependent

2. difficult to program3. it is error prone

4. it is difficult to modify

5. the programmer has to have expert knowledge of the computer

6. it is extremely difficult to learn and use

2nd Generation programming languages (Assembly Language)They use symbols and codes to represent program instructions instead of binary digits. The

resulting program still directly instructs the computer hardware therefore not easily portable.

Advantages

1. It is easier to correct errors and modify program instruction

2. They have the same execution efficiency as machine language3. Easy to understand and save a lot of time and effort of programmer

4. There is no worry about address

Disadvantages

1. They are still machine dependent

2. Knowledge of hardware is required 3. They are still time consuming 4. Program execution takes longer than machine language

3rd

generation programming languages (Procedural language)

They are easier to learn and use than were the earlier generations. While not directly

manipulating specific hardware components, they must still give the computer detailed

instructions of how to reach the desired results. They incorporate great use of english likeinstructions which are easier to learn and use. Examples include COBOL, FORTRAN, C, and

PASCAL.



40 Gabriel©

Procedural programming languages offer very little control and flexibility. They are portable.

4th

generation programming languages (non-procedural language)They are much easier to use and more English like than procedural languages. Its programs tell

the computer what it needs to accomplish but do not provide detailed instructions as to how to

accomplish it. They concentrate on the output and not procedural details. They can be used by

people who are not computer specialists e.g. C++, VISUAL BASIC, POWER BUILDER.

Object oriented programming languages

OOP was first introduced in 1967 by developers of a programming language named SIMULA 67.The basic idea behind OOP is that programming languages are used for simulating real world

problems on computers. OOP’s consist of objects that include descriptions of data relevant to the

object as well as the operations that can be done on that data.e.g query languages, report

generators, application generators

Features of OOP’s

1. There is extensive use of graphical objects2. There are features that allow easy program coding, error detection and correction

3. In order to write code, one double clicks on an object and selects the event for which they arewriting code.

Advantages

1. Program coding is made easier 2. Error correction is made easy

3. Writing a program or application takes less time compared to procedural.

4. It is easier to learn than procedural

5. They are portable

6. The programmer does not need to be an expert on the internal workings of a computer

7. Programs made using OOP’s are user friendly Disadvantages1. Interface design takes more time

2. One has to master all usable objects and event procedures in order to create an effective

application

3. Programs made using OOP’s occupy much more storage space than procedural languages

4. In some cases they are difficult to learn and use



Gabriel© 41

F:DATA PROCESSING

Definitions Data – Basic facts about the activities of the business. E.g. number of hours worked by

an employee on a particular machine.

Information – Data which is summarized in the way you want it, so that it is useful to

you in your work. It’s the end product of data processing. Must be accurate, timely,

complete, concise and relevant. Data Processing – Collection and manipulation of items of data to produce meaningful

information. It’s the process of transforming raw data into meaningful output i.e.

information.

Data processing can be done manually using pen and paper, mechanically using simple

devices like typewriters or electronically using modern data processing tools such as

computers.

Electronic data processing has become so popular that the manual and mechanical

methods are being faced out.

Factors determining the methods of data processing

a. Size and type of business.

Methods of producing the information largely depend on the size and type of business. In a

very small company, one person can be able to produce all the necessary information.However as the company increases in size, more people and aids e.g. calculators and small

computers will be needed. Large volumes of data and information will require the use of

large computers.

b. Timing aspects.

Some information requirements are less time critical than others. The timing requirement forinformation will have a considerable bearing on the methods and equipment needed to

provide it.

c. Link between applications.

Where data is needed for more than one information requirement, a different method of

processing it may be suggested.

Stages of data processingFrom the source documents.

a. Preparation of data for inputData is checked for correctness and validity i.e. transcription and they are also sorted.

b. Input of dataThe collected data is converted from human readable to machine readable form. The

conversion takes place in the input device.

c. ProcessingThe transformation of input data by the C.P.U to a more meaningful output (information).



42 Gabriel©

d. OutputThe production of the end product. The information can then be distributed to the target

group or stored for future reference.

Data CollectionData collection is getting the data from the point of its origin (source documents) to the

computer in a form suitable for processing. Also referred to as data gathering or fact finding.

Tools that help in data collection include source documents such as forms, data capture

devices e.g. digital camera e.t.c.

Stages of data collection

a. Data creation

It’s the process of putting together facts in an organized manner.

There two basic alternatives;

Source documents – A great deal of data still originate in the form of manually prepared

documents.

Data capture – Data is produced in machine-sensible form at source and is read directly bya suitable device e.g. a bar code reader.

b. Data transmissionThis depends on the method and medium of data collection adopted:

If computer is located at a central place, the documents will be physically transmitted i.e. by the postman or courier services.

It’s also possible for data to be transmitted by means of telephone lines to centralcomputer. In this case no source documents would be involved in the transmission

process.

c. Data preparation

This is the transcription (conversion) of data from the source documents to a machine-readable form.

Data collected using devices that directly capture data in digital form don’t require

transcription.

d. Data conversion

Data may need to be converted from one media to another e.g. from floppy disk to hard diskfor input to the computer.

e. Input validationData entered into the computer is subjected to validity checks by a computer program before

being used for processing.

f. SortingThis stage is required to re-arrange the data into a sequence required for processing. It’s a

practical necessity for efficient processing of sequentially organized data in many

commercial and financial applications.

g. Control



Gabriel© 43

It’s not really a stage because control is applied throughout the whole collection.

Data collection media and methodsa. On-line transmission of data from source e.g. Data Direct Entry (DDE)

b. Source document keyed directly keyed directly into diskette (key-to-diskette).

c. The source document itself prepared in machine-sensible form using character recognition

techniques.

d. Data capture devices.

e. Portable encoding devices.f. Source data captured from tags, plastic badges or strips.

g. Creation of data for input as a by-product of another operation.

Controls

Objectives of controls

i. To ensure that all data is processed.

ii. To preserve the integrity of maintained data.iii. To detect, correct and re-process all errors.

iv. To prevent and detect data.

Importance of controls

They must be instituted early as possible in the system. The quality of input data is of vitalimportance to the accuracy of output. Everything possible must be done to ensure that the data

are complete and accurate just before input to the computer.

Types of controls

a. Manual controls

b. Data preparationc. Validation checks

d. Batch controls

e. Other controls

a. Validation checks

These are attempts to build into the computer program powers of judgement so that incorrectitems of data are detected and reported.

These check s can be made in two stages:

Input– When data is first input into the computer, different checks can be applied to prevent errors going forward for processing. For this reason, the first computer run is often

referred to as validation or data vet. Updated – Further checking is possible when the data input are being processed.

The following are the main types of validation checks that may be used: Presence - Data are checked to ensure that all fields are present. Size - Fields are checked to ensure that they contain the right number of characters. Range - Number of codes are checked to ensure that they are within the permissible

range.

Character check - Fields are checked to ensure that they contain only characters of the

correct type e.g. no letters in numeric field.



44 Gabriel©

Format - Fields are checked to ensure that they are of the correct format. Reasonableness - Quantities are checked to ensure that they are not abnormally high or

low. Check digits – Use of a check digit enables a number to be self-checking. It’s a means of

ensuring that a number (e.g. a customer account number) maintains its validity.

b. Manual controls

Even in advance systems, considerable checking of the source documents is often necessary.

Such checks may be: Scrutiny to detect:

i. Missing entries.

ii. Illegal entries.

iii. Illogical or unlikely entries. Reference of the document to stored data to verify entries. Re-calculating to check calculations made on the document.

Types of errors during data collection.

a. Missing source documents.

b. Source documents on which entries are omitted, illegible or dubious.

c. Transcription errors e.g. errors in copying data from one form to another.

d. Data preparation errors e.g. errors made when keying onto diskette.

e. Program faults.

f. Machine hardware faults.

Types of data or computer files

Computer files – a collection of information initially created in memory and then stored with afile name on a secondary storage.

Are of two types:

- Command files - Contains program executable code that computer reads and uses as

instructions to prepare a task.

- Text/data files - Contain standard alphanumeric information that has been entered into

the file via an application program such as word processor, spreadsheet, database e.t.c.

Types of files

Master file

Main file that contains permanent data against which transactions are processed.Contain:

o Reference data- tends to be relatively permanent and which is processed by amending

i.e. making occasional changes in the form of insertion of new records, deletion or

alteration of existing records e.g. personnel details.

o Dynamic data – Changes frequently and is processed by updating i.e. changing values

of various fields e.g. earnings and deductions.

Transaction/movement filesIncludes input and output files for holding temporary incoming and outgoing data.



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Used to update dynamic data on master files.

Reference fileIt’s a file with a reasonable amount of permanency.

Used for look up or reference purposes e.g. PAYE deductions.

Report file

Set of records extracted from data in master file used to prepare report which can be printed

at a later date.Stores relatively permanent records extracted from the master files or generated after

processing.

Back up/History file

Holds copies of data or information from computer storage.

Retained for historical use or back up.

Dump/work fileUsed to hold data for security and recovery purposes or for temporary storage whilst otherwork is being carried out e.g. total earnings and deductions calculations (payroll processing).

Sort fileMainly used where data is to be processed sequentially in a sequential process.

Data Storage Hierarchy

It normally consists of the following six levels;

1. Bit. The smallest item of data is a single binary digit (a bit), either 0 or 1.

2. Character. Multiple related bits are combined to form a character. A bit is the basic unit of primary and secondary storage, and a character is the basic unit for human conception.

3. Field. It’s a meaningful collection of related characters.

4. Record. Multiple related fields are combined to form a record.

5. File. Multiple related records are combined to form a file. A file is a number of related

records which are treated as a unit. Every record in a file has the same set of fields. Each

record in a file is identified, for storage and retrieval purpose, by a key field whose contents

are unique for each record in a file. In case of an employee file, employee-code field mayserve as the key. In case of an employee file, employee-code field may serve as the key

field.



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6. Database. Multiple related files are integrated to form a database. A database is a collectionof logically related data elements from multiple files.

Standard methods of organizing dataTwo standard methods for organizing data are:

- File-oriented approach

- Database-oriented approach

File-oriented approach was the traditional method and has largely been replaced today by the

database-oriented approach.

File-oriented approachIn this method, an application’s data is organized into one or more files and the application

program processes the data stored in these files to generate the desired output.

This method of organizing data is simple, inexpensive and usually easy to use.It however suffers the following limitations:

1. Limited query flexibility. In file-oriented approach, the records are organized

according to a key field. As long as we search records based on key field value, thequery can be processed quickly.However, when the key field is not relevant to the

information needed, the entire field has to be searched.2. Data redundancy. This is the repetition of the same data items in more than one file.

In file-oriented approach, the same data items are often included in many different

files. This leads to increase in cost of data entry and data storage. It also leads to data

integrity problem.3. Data integrity problem. Data integrity is the consistency of the data in all files, i.e.

when some changes occur in a data item, every file which contains that field, should

be updated to reflect the change for consistency. For example, when a data item

changes, if all files are not updated correctly, there may be frequent discrepanciesamong reports produced from different files, causing confusion.

4. Lack of program/data independence. In file-oriented approach, the application programs usually contain data format statements that precisely define each data fieldto be processed. This often results in different files having the same data item stored

using different data formats. Data dependence occurs when the data is dependent on

the application. Due to data dependence problem, whenever there is need to add,

delete, or change data formats, the application program must also be changed. Data

dependence problem also causes incompatibility among data files from differentapplications due to which these data files cannot be linked, if such a need arises.

5. Limited data security flexibility. A file-oriented approach normally offers file-level

data security feature i.e. data access restrictions can be enforced only for an entirefile, not for a record or a record or a field of data item.

Database-oriented approachIn this approach, data from multiple related files are integrated together in the form of

a database, with the following properties:

1. It provides greater query flexibility.

2. It reduces data redundancy.3. It solves data integrity (inconsistency) problem.



Gabriel© 47

4. It makes data independent of the application programs i.e. fields can beadded, changed and deleted from the database without affecting existing

programs.5. It also includes data security features at database level, record level, and

even at field level to provide greater flexibility of restricted data access.

File organization1

This is the arrangement of records within a particular file.

File organization is very important because it determines the methods of access efficiency and

flexibility.

File organization methods

a. Sequential file organization

Records are stored and accessed in a particular order using a key field. Retrieval requiressearching sequentially through the entire file word for word from the beginning to the end.

e.g. if the record required is the twentieth record on the file, in order to get it into storage to process it the computer will first have to read in all nineteen preceding records. The principle

storage medium for sequential files is magnetic tapes.

Sequential file organization is the most efficient and economical file organization in case ofapplication in which there is a large number of file records to be updated at regular scheduled

intervals.

Applications such as payroll processing and monthly bill processing are processed in this

manner.

Advantages of sequential files1. They are conceptually simple to understand and use.

2. They are also easy to organize and maintain.

3. They need relatively inexpensive input- output media and devices for their storage

and processing.

4. They are most efficient and economical to use in applications in which the activity

ratio is high(most records are changed during update runs)

Disadvantages of sequential files1. They are very inefficient and uneconomical for applications in which the activity

ratio is very low.

2. Since an entire sequential file may need to be read just to retrieve and update fewrecords, accumulation of transactions into batches is recommended before processing them. Hence, the use of sequential files is limited to a batch-processing

environment.

3. Because of the need to accumulate transactions into batches before processing them,

sequential processing precludes the possibility of up-to-the-minute data.

4. Sequential processing require the files to be sorted before processing i.e. both the

transaction and master files must be sorted and placed in the same sequence before processing.

1 Very important



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5. Sequential processing often leads to data redundancy problem, since the same datamay be stored in several files sequenced on different keys.

b. Serial file organizationRecords in a file are accessed one after another.

c. Random/direct file organization

Records are stored in the disk at random but are accessed directly.Many applications require up-to-the-minute timeliness of data. The users of such applications

cannot afford to wait for the transactions to be accumulated to batches and then processed

together. Such applications require a transaction to be processed immediately as and when it

occurs. Examples of such applications are airlines or railway reservation systems, teller

facility in banking applications, systems for enquiring whether a certain item is in stock in a

store e.t.c. For such applications, the use of random/direct file organization is recommended,

in which the desired record pertaining to the current transaction at hand can be directlylocated by its key field value, without having to search through a sequence of other records.

The principal storage medium is magnetic/optical disc.Direct file organization uses an address generating function to convert a record key value into

a storage address on the disk on which the file is stored.

Advantages of direct files1. Given the key, any record can be quickly located and retrieved directly, without the

need for a sequential search of the file.

2. Transactions need not be sorted and placed in sequence before processing.

3. Accumulation of transactions into batches is not required before processing them.

They may be processed as and when generated.4. It can support interactive online applications, which need to provide up-to-the-

minute information in response to inquiries from users.

5. If required, it’s also possible to process direct file records sequentially in a record

key sequence.

Disadvantages of direct files1. They require relatively expensive hardware and software resources because they

must be stored on a direct-access storage device, such as a disk.

2. Due to address generation overhead involved, they are less efficient and economical

than sequential files for use in sequential applications with high activity ratio (The

ratio of the total number of records in a transaction file and the total number ofrecords in the master file).

3. Special security measures are often necessary for online direct files, which are

simultaneously accessible from multiple online stations.

d. Indexed sequential files

There two types of files involved:

- The data file which contains records stored in the file and- The smaller index file which contains the key and disk address of each record stored in

the data file.



The records of the file can be stored in a random sequence, but the index table is in sortedsequence on the key value. This provides the user with a very powerful tool. Not only can the

file be processed randomly, but it can also be processed sequentially.

Advantages of indexed sequential files1. They can be quite efficiently used for sequential processing of high activity ratio

applications.

2. They can also be used quite efficiently for direct access processing of low activity

ratio appliances.

Disadvantages of indexed sequential files1. They require relatively expensive hardware and software resources because they

must be stored on a direct-access basis, such as a disk.

2. They require more storage space than other types of files because of the need for

index file.

3. When used for direct access online applications, access to records may be slowerthan direct files.

introduction to computers-comprehensive

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