Introduction to Computer System

Introduction to Information Technology

Unit 1: Introduction to Computer System

Information Technology:

IT is the techniques used in Information System. An information system collects, processes, stores, analyzes, and disseminates information for a specific purpose. Communication is the backbone of IT. IT can be defined as the implementation of Information Science where

Information Science is a set of algorithms, principles and theories. Computer System, Internet, Telecommunication systems are the information technology we use. Information systems are scattered throughout organizations, often in several locations and sometimes in two or more organizations. IT is implemented here to relay the information between these locations. Not only the organization but also the individual today is dependant on IT for career development and education. Education Institutions today provide distant education and online examinations. GIS has emerged due to the development in IT. Scientists now are able to acquire geographical information from the satellites.

Evolution of Information Processing Information Processing evolved due to the growth of national and international organizations. Since the early computing days, as costs declined and computer technologies improved, computers have been used to support managerial and other organizational activities of every sort.

Scopes/ Application field of Information System

  • Telecommunication
  • Internet
  • GIS
  • Education
  • Security System
  • E-Governance
  • Medicine
  • Scientific Research


1.1 Introduction to Computers

A computer is a programmable electronic machine. It takes raw facts as input, process these and gives the final output which is the result of processing. It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program).


1.2. Classification of Digital Computers (Types of Computers)

Computers can be classified by their size and power as follows:

  1. Super Computers
  2. Mainframe Computers
  3. Mini Computers
  4. Work Stations
  5. Micro Computers/ Personal Computer

Super Computers

 They are the computers with the most processing power. The primary application of supercomputers has been in scientific and military work, but their use is growing in business as their prices decreases. They are especially valuable for large simulation models of real world phenomena, where complex mathematical representations and calculations are required or for image creation and processing. They are also used in weather prediction, design aircraft( Boeing 777), motion picture like star wars and Jurassic Park) They operate generally at 4 to 10 times faster than the next most powerful computer class., the mainframe.


  1. a) Mainframe Computers

  • They are less powerful and generally less expensive than supercomputers.
  • Large corporate use mainframe computers for centralized data processing maintaining large
  • databasesApplication than run on a mainframe can be large and complex, allowing for data andinformation to be shared throughout the organization.
  • Examples: Airline Reservation System, Corporate Payroll, Student Information etc.
  • A mainframe system may have anywhere from 50megabytes to several gigabytes of primary storage.
  • Secondary storage may use high capacity magnetic and optical storage media with capacities in the gigabytes to terabyte range.
  • Typically, several hundreds or thousands or online computers can be linked to a mainframe.
  • Advance mainframe performs more than 1,000 MIPS and can handle up to one billion

transactions per day.

  1. b) Mini Computers

  • Also called midrange computers, are relatively small, inexpensive and compact computers that perform the same functions as mainframe computers but to limited extent.
  • They are designed specially for accomplishing specific tasks such as process control, scientific research, and engineering applications.
  • IBM is the market leader in minicomputers with its AS/400 series of computers.
  • Larger companies gain greater corporate flexibility by distributing data processing

with minicomputers in organizations units instead of centralization at one place.

  • They form the network.
  1. c) Workstations
  • Computers vendors originally developed desktop engineering workstations or to

provide the high levels of performance demanded by engineers.

  • They are based on RISC (Reduced Instruction Set Computing) architecture and

provide both very high speed calculations and high resolution graphic displays.

  • The distinction between workstation and personal computers is rapidly blurring.
  • The latest PC s has the computing power of recent workstation.
  1. d) Micro Computers

These are also called PCs and are the smallest and least expensive category of general

purpose computers. Micro computer ranges from palmtops to Desktop computers.

Laptops/ Notebooks are very popular now a day. Microprocessor is the core part of the

Micro computers which forms the CPU.

1.3. Anatomy of Digital Computers

Functions and Components of a Computer:

To function properly, the computer needs both hardware and software. Hardware consists of the

mechanical and electronic devices, which we can see and touch. The different parts of the

computer are Processor (CPU), Input devices, Output devices, Storage devices and Memory

devices. The software consists of programs, the operating systems and the data that reside in the

memory and storage devices.

A computer does mainly the following four functions:

  •  Receive input – Accept information from outside through various input devices like the
  • keyboard, mouse, etc.
  •  Produce information – Perform arithmetic or logical operations on the information.
  •  Produce output – Communicate information to the outside word through output devices
  • like monitor, printer, etc.
  •  Store information – Store the information in storage devices like hard disk, floppy disks,
  • etc.

Computer hardware falls into two categories: processing hardware, which consists of the central processing unit (CPU), and the peripheral devices. The CPU, as its name implies, is where the data processing is done. Peripheral devices allow people to interact with the CPU. Together, they make it possible to use the computer for a variety of tasks.

Explain CPU  and its different components: CU, ALU and MU.


An instruction is fetched from primary storage by the Control Unit The Control Unit decodes the instruction The ALU receives the data and the instruction and performs the calculation or comparison The result is stored in primary storage which is sent to the proper output device.

1.4. Computer Architecture

History: Describe from Pascaline to the first generation computers:


In 1642, 19 year old French mathematician Blaise pascal invented a mechanical adding-machine called pascaline. The numbers were entered by means of add and subtract. It had 8 wheels and each wheel had 10 digits from 0 to 9. Stepped Recknor In 1671, German mathematician Gothfried von Leibnitsz invented an improved and strong computing machine called “stepped Recknor” which could multiply, divide and workout square roots apart from addition and subtraction. The machine also had handle and gear.

Analytical Engine

In 1833, Charles Babbage, (English mathematician) developed Analytical Engine which was a kind of a general purpose computer designed to solve any arithmetical problems. It was significant in a way that it had most of the elements present in today‟s digital computer systems, that‟s why he‟s called “Father of modern computer science.”


Lady Ada Augusta, disciple of charles Babbage, after his demise developed several programs forperforming mathematical calculations on Analytical engine. She is considered as the firstprogrammer in history and has to her credit a computer language called ADA named after her.

Dr. Herman Hollerith

In 1890AD, Herman Hollerith designed a system to record census data. The information was stored as holes in punched cards, which were interpreted by machines with electrical sensors.


In 1944 Howard Aiken completed mark I. It was an electromechanical computer which was 51ft. long, 8 ft. height, and 3 ft wide and consisted of 18000 vacuum tubes. This consisted of 7 lakh 50 thousand parts and 500 miles long wire.

Electronic Numerical integration and calculator (ENIAC) – 1946 A.D.

ENIAC was the first electronic computer developed by John Mauchly and John presper Eckret in

  1. It could do 5000 additions per second. It was extremely huge, used 19,000 vacuum tubes, occupied an area of 150 sq. meters, weighed about 30 tons and required about 130 kW of power.


In 1952, Electronic Discrete Variable Automatic Computer (EDVAC) was developed by John Mauchly and John Presper Eckert with the help of A. Burks and Neumann. This machine was used to store the data and information as well as the instructions.

John Mauchly and Eckert founded their own company in 1946 and began to work on Universal Automatic Computer (UNIVAC): general purpose commercial computer

  • in 1951 It was the first commercially used electronic computer in the world.
  • In 1958, the first computer to use the transistor as a switching device, the IBM 7090, was
  • introduced.
  • In 1964, the first computer to use Integrated circuits (IC), the IBM 360 was announced.
  • In 1975, the first microcomputer, the Altair, was introduced. In the same year, the first
  • Supercomputer, the Cray-1 was announced.



RISC (Reduced Instruction Set Computer) processors are designed for speeding up the processing power of the computer making the chip as simple as possible so that it uses less space and shorter design cycle. It is possible to use the technique of pipelining using RISC processors which gives the immense processing power.

The advantages of RISC processors are as follows:

  1. Speed: Due to simplified instruction set RISC processors are 2 to 4 times faster.
  2. Simpler hardware- Because of simpler instruction set the RISC processor uses much less chip space, as a result extra functions are also placed in the same chip.
  3. Shorter design cycle- Because of simple hardware and less instruction per task, the RISC processor uses very short machine cycles.

CISC (Complex Instruction Set Computer) processors use microcode, build rich instruction sets

and build high-level instruction sets and these were the building blocks until the late 1980s and

are still in major use today.

Some characteristics are:

  1. Complex instruction-decoding logic, driven by the need for a single instruction to support multiple addressing modes.
  1. A small number of general purpose registers.
  2. Several special purposes register.


Advantages of CISC:

  1. Microprogramming is as easy as assembly language to implement, and much less expensive than hardwiring a control unit.
  1. The ease of micro-coding new instructions allowed the designers to make CISC machines upwardly compatible, i.e. a new computer could run the same programs as earlier computers.
  1. As each instruction became more capable, fewer instructions could be used to implement a given task.
  1. Because micro-program instruction sets can be written to match the constructs of highlevel languages, the compiler does not have to be complicated.

The disadvantages of CISC:

  1. The instruction set and chip hardware became more complex with each generation of computers.
  1. The instructions set were lengthy and took more time to execute, slowing down the overall performance of the machine.
  1. Many specialized instructions aren‟t used frequently enough to justify their existence.


1.5. Number System

Refer to the exercise covered during the class. Binary Subtraction using complement‟s method is left for further discussion later after the Final Evaluation exam.

Memory Units:

Memory units are the internal storages areas in a computer. These are in the form of chips. Usually we classify the computer‟s memory into two categories: RAM and ROM.

RAM (Random Access Memory):

This is the main memory of the computer. This is also found in other devices like printers. This memory holds data as long as the electricity is supplied and therefore referred to as volatile memory. There are two basic types of RAM: (i) Dynamic RAM (DRAM) and (ii) Static RAM


Dynamic RAM needs to be refreshed thousands of times per second. Static RAM needs to be refreshed less often, which makes it faster; but it is more expensive than dynamic RAM.

ROM (Read Only Memory)

It is a non-volatile memory. The data is prerecorded in ROM. The program stored in ROM is known as Firmware and is programmed by the manufacturer. Once data has been written onto a ROM chip, it cannot be removed and can only be read. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer.


1.6. Auxiliary Storage Units

Hard Disk:

  • A Hard disk is internal hardware which stores and provides access to large amounts of information.
  • Hard disks have much greater data capacity and are much faster to use than floppy disks.
  • Usually, it is a fixed disk, permanently sealed in the drive.
  • Most new computers include an internal hard disk that contains several gigabytes or terabytes of storage capacity.
  • The head of hard disk that reads the data floats over the hard disk‟s surface, while the head of the floppy disk touches the disk‟s surface while reading or writing data.


  • Hard disk is a flat, circular, rigid plate with a magnetizable surface on one or both sides of which data can be stored.
  • Hard disks are rigid aluminum or glass disks about 3.5” in diameter in a personal computer, and smaller in a laptop.
  • Data is transferred magnetically by a read/write head.
  • A hard disk is made of metallic disk coated with metallic oxide on both sides.
  • To increase the storing capacity, several disks (platter) are packed together and mounted on a common drive to form a disk pack.
  • A hard disk can have more than 1000 tracks per surface and contain 17 sectors per track.


Optical Disk

  • An emerging technology that many expect will have a profound impact on mass storage strategies in the 1990s is the Optical Disk.
  • With this technology becomes laser beams to wrote and read data at incredible densities.
  • Thousand of times finer than the density of a typical magnetic disk.
  • Data are placed onto optical disks with high-intensity laser beams that burn tiny holesinto the disk‟s surface.
  • Optical disk systems have recently started to become widely used on microcomputer systems.
  • So, it is a storage medium from which data is read and to which it is written by lasers. Store much more data in portable magnetic media.
  • There are three basic types of optical disks.
  • CD-ROM (compact disk read only memory)
  • WORM ( write once read many)
  • These three are not compatible with one another.
  • WORM (Write-one Read-many)
  • With a WORD disk, you can write data, but only once and then you can read number of times.
  • ERASABLE Optical (rewritable & erasable)
  • Can be read to, written to and erased just like magnetic disk.
  • CD-R (Compact Disk Recordable)
  • CD-RD (Compact Disk Rewritable)
  • DVD (Digital Versatile Disc)
  • Initial storage capacity of 4.7GB digital information on a single sided, single layer.
  • Diameter & thickness is same as CD-ROM.

Magnetic Tape:

  • Magnetic tape is a plastic tape with a magnetic surface for storing data as a series of

magnetic spots.

  • Magnetic tape has been one of the most prominent secondary storage alternatives.
  • Magnetic tape is the most commonly used sequential access secondary storage medium.
  • It is available in the form of cassettes, real & cartridges.
  • Among these three, Reels are the most popular storage secondary media.
  • Magnetic tape is a plastic ribbon coated on one side with iron oxide that can be


Floppy Disk:

Floppy disk is a soft magnetic disk. Floppy disks are being replaced by pen drives now a days. Foppy disks are slower to access than hard disks and have very less storage capacity.



1.7. Input Devices

How does a Keyboard Work


Computer keyboards are an input device. They put the information a person types into aprogram on the computer. Most keyboards have 80 to 110 keys. The numbers and letters on the keyboard are displayed keycaps–these are the buttons that are pressed when a person types. The layout of the numbers and letters are the same on every keyboard and they are referred to as the QWERTY.


Key matrix

The inside of the keyboard is like a mini-computer and consists of a processor and circuits. These transfer the information to the processor inside of the computer. Inside of the keyboard’s processor resides the key matrix. The key matrix is a grid of circuits. These circuits are individually placed under each key. When a key is pushed, it pushes the switch on the circuit board underneath the key causing an electrical current to pass through the circuit and into the processor. When the current passes through, the switch vibrates, signaling the processor to read it. Depending upon the working principle, there are two main types of keys, namely, capacitive and hard-contact


Capacitive Key

On the underside of a capacitive key, a metal plunger is fixed which helps in activating the circuit flow. When a capacitive key is pressed, the metal plunger applies a gentle pressure to the circuit board. The pressure is identified by the computer and the circuit flow is initiated, resulting in the transfer of information from the circuit to the currently installed software.


Hard Contact Key

A hard contact key is attached with a metallic plate that helps in connecting the circuit board. When the hard contact key is pressed, it pushes a metallic plate, which in turn touches the metallic portion of the circuit plate. This overall process of completing a circuit results in a circuit flow, allowing the transfer of the message to the central processing unit (CPU), which is further transmitted to the software.

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