The document provides an introduction to computer systems and their components. It defines a computer system as a complete, working computer along with necessary software and peripheral devices. The key components of a computer system are described as the input devices, output devices, system unit, storage devices, and communication devices. The document also discusses the different types of computers including microcomputers, minicomputers, mainframe computers, and supercomputers. It defines each type based on their size and processing power.

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What is System?
A system is a set of related components that interact with each other to perform some
specific tasks. A set of detailed methods, procedures and routines created to carry out
a specific activity, perform a duty, or solve a problem. An organized, purposeful
structure that consists of interrelated and interdependent elements, components,
entities, factors, members, parts etc. These elements continually influence one another
(directly or indirectly) to maintain their activity and the existence of the system, in
order to achieve the goal of the system.
Characteristics of System:
 Structure
 Behavior
 Inter Connectivity
Subsystems:
 A major part of a system which itself has the characteristics of a system,
usually consisting of several components.
 Set of elements, which is a system itself, and a component of a larger system.
Computer System:
A complete, working computer along with software and peripheral devices that are
necessary to make the computer function is called Computer system. Every computer
system requires an operating system to operate.
What is Computer?
An electronic machine that can accept data (input), manipulate the data according to
specified rules (process), produce results (output), and stores the results for future use.
Computer in Latin means "to consider" or 'to compute'. Some experts have coined a
word for it 'INFORMATIC', the science of information processing i.e. methods of
recording, manipulation and retrieving information. So it is a calculating device with
some special characteristics and abilities like perform complex and repetitive
calculations rapidly and accurately, make decisions and automatically correct or
modify by providing signals, certain parameters of a system under control,
communicate with users through terminals etc. A computer is a programmable
machine. The two principal characteristics of a computer are: it responds to a specific
set of instructions in a well defined manner and it can execute a prerecorded list of
instructions (a program).
A computer is a general purpose device that can be programmed to carry out a fixed
set of arithmetic or logical operations. Since a sequence of operations can be readily
changed, the computer can solve more than one kind of problem. Usually, a computer
consists of at least one processing element, typically a central processing unit (CPU) and
some form of memory. The processing element carries out arithmetic and logic operations,
and a sequencing and control unit that can change the order of operations based on stored
information. Peripheral devices allow information to be retrieved from an external source, and
the result of operations saved and retrieved.
Data, Information and Knowledge:
Data: Collection of raw facts and figures.
Information: Processed form of data which is meaningful.
Knowledge: Appropriate collection of information. Combination of data, information
and experience.
Information Processing Cycle:
 Series of input, processes, output and storage.
 A computer often holds data, instructions and information for future use.

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The Components of a Computer:
 Input devices
 Output devices
 System unit
 Storage devices
 Communications devices
Importance of Computer:
As we hurtle towards the 21st century, we must accept the certainty of a computer
revolution in the near future. It is an undividable part of development, as
demonstrated by other countries. Computers are no longer luxury or the sole property
of the advanced countries. Their appropriate uses can help us solve the unique
problems of a developing country and bring about the desired changes in increasing
literacy, optimizing resources, increasing efficiency, productivity and quality. Already
computers have become such an important part of our lives, in airports, banks, railway
stations and every well equipped modern office.
As computer continues to reproduce in ever increasing numbers across large segments
of Government, business and industry, the common man is beginning to believe
hesitantly that computers can actually deliver a good part of the promise that they had
offered. Society is gradually accepting the fact that computers will indeed change the
manner, in which the things are done.
Computers can significantly save valuable man hours by helping people through
communication to make reservation of tickets, operate their bank accounts, to pay for
electricity water and telephone bills, insurance premium and also do routine shopping.
Trains can be operated automatically by computers and traffic signals are computer
coordinate to produce best traffic patterns, increase reliability and safety and generally
provide for more efficient services. In areas of agriculture and irrigation, computers
are making possible better matching of soil characteristics and crop. This coupled
with better use of resources like water, fertilizers and sunlight and more precise
prediction of monsoons can help in increasing crop yields manifold.
Computer in health is bringing new hope for the sick. In areas of health and medicine,
expert systems and data bases on blood groups availability, eye banks medical history
of patients etc, can bring about a marked improvement in our health services. Expert
system can help in more accurate diagnosis of ailments 'Hospital Information
Systems' can help improve the efficiency of our hospitals reduce mortality and death
rates and in general provide better and speedier health care to our people.
While this realization is gaining firmer ground in areas like the utility services,
railways, airlines, agriculture, health etc., as well as organization control, there is area
where the role of computers as the prime agents of change has still not been
recognized. That is the area of education.
The number of illiterates at present is higher than that at independence. To tackle a
problem of such huge proportions, it is essential that a modern aids offered by
Information Technology is made use of to spread education to the rural areas where
most of the illiteracy is concentrated. Computer based lessons developed in various
subjects by experts in that area could be used to educate the masses. The computer is
a rapidly evolving tool that can now deal quite effectively with all fine forms of
information that man deals with for better education are data, text, image, graphics
and voice.
One thought can take place in our minds for a moment that 'the computer will replace
the teacher that would be a suicidal thought. But we should fully accept the reality
that the computer will fundamentally change the manner in which teaching-learning

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processes take place. The role of the teacher will undergo a fundamental change.
From being a simple "information dumping machine", the teacher will once again rise
to the height of being a mentor, philosopher and guide developing, instilling values,
ideas, creating challenges and nurturing feelings, sentiments and empathy in young
minds. In the wider prospective, these are what are required for building a strong
nation, intellectually, spiritually and economically.
In the most important area of government administration, to enable administration
take the right decision at the right time, accurate, relevant and up-to-date information
should be made available to them. Modern computerized communication network can
significantly help bureaucracy cut its red tape.
Therefore, computers are equal with development. With appropriate computer usage
and quality of life applications, Pakistan will be able to effectively tackle its unique
problems. The entire society will undergo a transformation and what would emerge is
a society that is more intellectually aware and which values its time, intellect and
dignity. A society armed with computer expertise can meet with confidence the
exciting new Pakistan of tomorrow.
Advantages:
 It helps you automate various tasks that you cannot do manually.
 It helps you organize and store your bulky data and information in a better way.
 It has much more computing and calculating power than an ordinary human.
 It may help your work to be a lot easier.
 It may be the storage of your important data and files.
 It may be your hand book.
 It may help you solve problems faster than an ordinary human being can do.
 It has speed, storage, reliability, consistency and communications.
 It helps you to find useful information using the Internet.
 It helps in businesses, factories, offices, schools and homes.
Disadvantage:
 It destroys your social life and interactions with humans if you do not maintain the
balance.
 It may effect to the destruction of your eye sight due to radiation.
 It may damage your studies and life.
 Too much time in front of monitor may adverse effect your eye sight and can also
make you fat.
 The way it distracts and can deviate our thoughts and activities towards
unproductive activities.
 It could cause violation of privacy, impact on labor force, health risks, impact on
environment, distraction from work, and antisocial influences.
Generations of Computer:
1. First Generation Vacuum Tubes: (1942-1955)
2. Second Generation TRANSISTORS: (1955-1964)
3. Third Generation Integrated Circuits: (1964-1975)
4. Fourth Generation Microprocessors: (1975- PRESENT)
5. Fifth Generation Artificial Intelligence: (Present and Beyond)
1. First Generation Computers (Vacuum Tubes) 1942-1955:
The first generation of computers, characterized by vacuum tubes used in the duration
of 1942-1955.
Examples: ENIVAC (Electronic Numerical Integrator and Calculator) First
Electronic Computer UNIVAC (Universal Automatic Computer) First Digital

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Computer used in business and industries. Vacuum Tubes electronic tubes about the
size of light bulbs.
Advantages:
• Vacuum tubes were the only components available during those days.
• Vacuum tube technology made possible to make electronic digital computers.
• These Computers could calculate data in milliseconds.
Disadvantages:
• Very large in size.
• Consumed large amount of energy.
• Heated very soon due to thousand of vacuum tubes.
• Not very reliable.
• Air conditioning was required.
• Non-portable.
• Costly commercial production.
• Very slow speed.
• Used machine language only
• Used punch cards for input
• Not versatile and very faulty.
2. Second Generation Computers (Transistors) 1955-1964
Used Transistors. Transistors are developed in Bell Laboratories in 1947. The size of
computer decreases by replacing vacuum tubes by Transistors.
Examples:
IBM 7097 series, IBM 1400 Series
Transistor: A transistor is a semiconductor device used to amplify and switch
electronic signals and power.
Advantages:
• Smaller in size as compared to first generation computers.
• More reliable.
• Used less energy and were not heated.
• Better portability.
• Better speed and could calculate data in microseconds.
• Accuracy improved.
Disadvantages:
• Air conditioning was required.
• Constant maintenance required.
• Only used for specific purpose.
• Costly and not versatile.
• Punch cards were used for input.
3. Third Generation Computers (Integrated Circuits) 1964-1975
Used Integrated Circuits. First IC was invented and used in 1961. The size of an IC is
about ¼ square inch. A single IC contains thousands of transistors.
Examples:
IBM 370, IBM System/360
Advantages:
• Smaller in size as compare to previous.
• More reliable.
• Use less energy.
• Produce less heat as compare to previous.
• Better speed could calculate data in nanoseconds.
• Versatile to an extent.

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• Used fan for heat discharge.
• Low maintenance cost because hardware failure is rare.
• Totally General purpose.
• Good Storage, Less expansive, better accuracy. Key board and mouse for input.
Disadvantages:
• Air Conditioning was required.
• High sophisticated technology required for the manufacturing of IC chips.
4. Fourth Generation Computers (Microprocessors) 1975- PRESENT
Starts with the invention of Microprocessors. Microprocessor contains thousands of
ICs. Ted Hof creates first Microprocessor for Intel in 1971.
Examples:
Apple Macintosh & IBM PC
Advantages:
• More powerful and reliable then previous.
• Very small in size
• Less power consumption.
• Less heat generation.
• Used fan for heat discharge.
• No air condition is required.
• Totally General purpose.
• Less need of repairing.
• Cheapest among all the generations.
• Best speed to read instructions (One million per second).
Disadvantages:
• The latest technology is required for manufacturing microprocessors.
5. Fifth Generation Computers (Artificial Intelligence) Present and Beyond
Based on the technique of Artificial Intelligence (AI). Computers can understand
spoken words. Scientists are working to increase the speed of computers. The
advancement in modern technologies will revolutionize the computer in future.

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Types of Computer:
Computer types can be divided into 3 categories according to electronic nature.
1. Analog Computer
2. Digital Computer
3. Hybrid Computer
1. Analogue Computer:
Analogue types of Computer uses analogue signals that are represented by a
continuous set of varying voltages and are used in scientific research centers.
2. Digital Computer:
A computer that stores data in terms of digits (numbers) and proceeds in discrete steps
from one state to the next. The states of a digital computer typically involves binary
digits which may take the form of the presence or absence of magnetic markers in a
storage medium. In digital computers, even letters, words and whole texts are
represented digitally.
 0,1
 False true
 Low high
3. Hybrid Computers:
Designed to display the features and characteristics of both analog and the digital
computers. When the hybrid computers are used in the form of digital computers then
they are deigned to act as the controller for the operations carried out in the system.
When analog is taken into account then in that case the computer acts as a solution
provider for different problems that exit. By depicting both the feature, it is found to
be a beneficial computer.
Classification of Computer:
There are two types of classes:
1. Classes by Size
2. Classes by Functions
1. Classes by Size:
1.1 Microcomputers (Personal Computers)
1.2 Minicomputers (Midrange Computers)
1.3 Mainframe Computers
1.4 Supercomputer
1.1 Microcomputers (Personal Computers):
Microcomputers are the most common type of computers used by people today,
whether in a workplace, at school or on the desk at home. E.g.
1.1.1 Desktop Computers
1.1.2 Game Consoles Laptops
1.1.3 Notebook Computers
1.1.4 Palmtop Computers
1.1.5 Tablet PC
1.1.6 Programmable Calculator
1.1.1 Desktop Computers:
A desktop computer is a personal computer (PC) in a form intended for regular use at
a single location, as opposed to a mobile laptop or portable computer. Early desktop
computers are designed to lie flat on the desk, while modern towers stand upright.
Most modern desktop computers have separate screens and keyboards.

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1.1.2 Game Consoles Laptops:
Console games are more commonly referred to as video games. They are played on a
device specially made for game play called a video game console. The player interacts
with the game through a controller, a hand-held device with buttons and joysticks or
pads.
1.1.3 Notebook Computers:
A notebook computer is a battery- or AC-powered personal computer generally
smaller than a briefcase that can easily be transported and conveniently used in
temporary spaces such as on airplanes, in libraries, temporary offices, and at
meetings. A notebook computer, sometimes called a laptop computer.
1.1.4 Palmtop Computers:
A small computer that literally fits in your palm. Compared to full-size computers. A
computer that has a small screen and compressed keyboard and is small enough to be
held in the hand, often used as a personal organizer.
1.1.5 Tablet PC:
A tablet PC is a wireless, portable personal computer with a touch screen interface.
The tablet is typically smaller than a notebook computer but larger than a smart
phone.
1.1.6 Programmable Calculators:
A limited-function computer capable of working with only numbers and not
alphanumeric data. Programmable calculators allow the user to write and store
programs in the calculator in order to solve difficult problems or automate an
elaborate procedure.
1.2 Minicomputers:
Contemporary term for this class of system is midrange computer. Midrange system is
more powerful and larger than a work station computer. Servers typically support
several hundred and sometimes up to a few thousand connected computers at the
same time. It is use in smaller organizations. Initially these had category between
mainframe and personal computers. Now a days we use server machine instead of
mini computers. Such as the higher-end SPARC, POWER and Itanium -based
systems from Sun Microsystems, IBM and Hewlett-Packard.
1.3 Mainframe Computers:
It is used in large organizations. A very large and expensive computer capable of
supporting hundreds, or even thousands, of users simultaneously. Also it is called
enterprise servers. There are multiple processors in these computers (2,4,12). Banks
and shopping marts are interconnected through mainframe computers.
1.4 Super Computers:
All of the resources to tackle one problem Used for very complex operations for
example rocket launching, weather prediction, Aeronautics and testing of nuclear
weapons etc. Cray one 160 million instructions /second. It has160 trillion bytes
storage and 6 trillion bytes memory.
Comparison between Minicomputer, Mainframe & Supercomputer:
 In some ways, mainframes are more powerful than supercomputers as they support
more simultaneous programs. But supercomputers can execute a single program
faster than a mainframe.
 The distinction between small mainframes and minicomputers is vague, depending
really on how the manufacturer wants to market its machines.

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Hierarchy:
A system or organization in which people or groups are ranked one above the other
according to status or authority.
Hierarchy of Computers:
In the hierarchy starting with a simple microprocessor (watches) at the bottom
supercomputers at the top, mainframes are just below super computers.
Comparison Table:
Category of Computer Number of Simultaneous
Users
Size of Computer
Personal Computer
Desktop)
Fits on a Desk Usually one(more if net
worker)
Mobile Computer and
Mobile Devices
Fits on your lap or in hand Usually One
Game Console Small box or hand held
Device
One to Several
Server Small Cabinet Two to Thousands
Mainframe Partial room to full room
of Equipment
Hundreds to Thousands
Super Computer Full room of equipment Hundreds to Thousands
Embedded Computer Miniature Usually One
2. Classes by Functions:
2.1 Servers
2.2 Workstations
2.3 Information Appliances
2.4 Embedded Computers
2.1 Servers:
Server is a physical computer (a hardware system) dedicated to running one or more
such services (as a host) to serve the needs of users of the other computers on the
network.
Types of Server:
Depending on the computing service that it offers it could be:
2.1.1 Database Server
2.1.2 File Server
2.1.3 Mail Server
2.1.4 Print Server
2.1.5 Web Server
2.1.1 Database Server:
Provides database services to other computers as defined by the client-server model.
DBMS provide database server functionality. In a master-slave model, database
master servers are central and primary locations of data while database slave servers
are synchronized backups of the master acting as proxies, e.g. Oracle, DB2, SQL
server.
2.1.2 File Server:
Computer attached to a network with primary purpose of providing a location for
shared disk access, i.e. shared storage of computer files (such as documents, sound
files, photographs, movies, images, databases, etc.) that can be accessed by the
workstations that are attached to the computer network.

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2.1.3 Mail Server:
Every email that is sent passes through a series of mail servers. A complex series of
transfers takes place. Without this series of mail servers, email can be sent to the
email address of the same domain.
2.1.4 Print Server:
A print server, or printer server, is a device that connects printers to client
computers over a network. It accepts print jobs from the computers and send the jobs
to the appropriate printers. Print servers may support a variety of industry standard or
proprietary printing protocols including Internet Printing Protocol, Line Printer
Daemon protocol, NetWare,NetBIOS/NetBEUI, or JetDirect. A print server may be a
networked computer with one or more shared printers. Alternatively a print server
may be a dedicated device on the network, with connections to the LAN and one or
more printers. Dedicated server appliances tend to be fairly simple in both
configuration and features. Print server functionality may be integrated with other
devices such as a wireless router, a firewall, or both. A printer may have a built-in
print server.
2.1.5 Web Server:
Web server can refer to either the hardware (the computer) or the software (the
computer application) that helps to deliver web content that can be accessed through
the Internet. The most common use of web servers is to host websites, but there are
other uses such as gaming, data storage or running enterprise applications. The
primary function of a web server is to deliver web pages on the request
to clients using the Hypertext Transfer Protocol (HTTP). This means delivery
of HTML documents and any additional content that may be included by a document,
such as images, style sheets and scripts.
2.2 Workstations:
A workstation is a high-end microcomputer designed for technical or scientific
applications. Intended primarily to be used by one person at a time, they are
commonly connected to a local area network and run multi-user operating systems.
The term workstation has also been used to refer to a mainframe computer terminal or
a PC connected to a network. In networking, workstation refers to any computer
connected to a local-area network. It could be a workstation or a personal computer.
2.3 Information Appliances:
In information appliance or information device is any machine or device that is usable
for the purposes of computing, telecommunicating, reproducing, and presenting
encoded information in innumerable forms and applications.
2.4 Embedded Computers:
Embedded computers can be compared to "computers on a chip". All in one , so to
speak. You will find them in all kind of devices surrounding us where you need to
regulate something, control or check something e.g.
 Home automation devices e.g. Washing machines, Sewing machines, Microwave.
 Ticket machines at the subway.
 Cameras, clocks Cell phone, Video games, Global Positioning System.
 Automobiles, cars, motors.
 Mobile Devices Handheld Computers, PDA, Smart Phones, GPS.