class 11 chapter 1-2



A computer is a powerful logical tool which works by using programs given (written or coded) by user. In other words, a computer is an electric machine that can store, organize, find and manipulate information, do calculations and control other devices.


Computer can be defined as an electronic device that processes the input data according to the given set of instruction to give meaningful output.


Computer can be defined as an electronic digital and automatic machine which takes input from the user, process it, stores if necessary and give output in desired form.


Characteristics of a Computer



A large amount of data can be stored in a computer's memory. The storing capacity pf a computer is expressed in Bytes. A byte stores one character of information . The storage Characteristic of a computer has made it a special device. 

Data Measurement

Data Measurement




Single Binary Digit (1 or 0)



8 bits


Kilobyte (KB)

1,024 Bytes


Megabyte (MB)

1,024 Kilobytes


Gigabyte (GB)

1,024 Megabytes


Terabyte (TB)

1,024 Gigabytes


Petabyte (PB)

1,024 Terabytes


Exabyte (EB)

1,024 Petabytes


Computer performs complex calculation at a very high speed. Generally, the speed of a computer is measured in term of fraction of a second. Different term that are used to denote the speed are created. Because of those characteristic,they have been used in such field (e.g. satellite launching) where immediate result are expected.

Speed  Measurement










Micro second



Nano Second



Pico Second










If the program and data have no error, the result given by the computer will be 100% accurate. If mistake occurs in any calculation,they are due to manual error like feeding wrong data or mistake in the instrument given.

Once we give the appropriate instruction, a computer can perform the operation automatically. It carry on with the given task independently and continuously.

Computer  has a wide range of application area. It has been successfully used in different area like Education,  Science and Technology, Astronomy, Business, Medicine, etc. Hence the computer is a versatile device.

If any calculation is done one or a billion times, only the computer does it with the same speed and accuracy. Unlike the human beings, a computer never gets tired to do its task. Computer is a machine. Thus computer is capable of performing the required task repetitively without affecting its speed, accuracy and efficiency.

No feelings

Computer does not have feelings or emotions because it is a machine. It cannot make any decision based on experience, love, knowledge.

No I.Q

Computer has no intelligence to perform any task on its own like human being. Every instruction is given by human being to computer for performing the task.


IPO cycle


  Block Diagram of Computer

CR-rie.jpg CR-rie.jpg

                                   IPO and logical Diagram



Computers need to receive data and instruction in order to solve any problem. Therefore we need to input the data and instructions into the computers. The input unit consists of one or more input devices. Keyboard is the one of the most commonly used input device. Other commonly used input devices are the mouse, floppy disk drive, magnetic tape, etc.S

Storage Unit:

The storage unit of the computer holds data and instructions that are entered through the input unit, before they are processed. It preserves the intermediate and final results before these are sent to the output devices. It also saves the data for the later use.

memory are quite common.


1. Control Unit: It is responsible for directing and coordinating most of the computer system activities. It does not execute instructions by itself. It tells other parts of the computer system what to do. It determines the movement of electronic signals between the main memory and arithmetic logic unit as well as the control signals between the CPU and input/output devices.

2. Arithmetic logic Unit: ALU performs all the arithmetic and logical functions i.e. addition, subtraction, multiplication, division and certain comparisons. These comparisons include greater than, less than, equals to etc. The ALU controls the speed of calculations.

3. Registers: It is a special temporary storage location within the CPU. Registers quickly, accept, store and transfer data and instructions that are being used immediately (main memory hold data that will be used shortly, secondary storage holds data that will be used later). To execute an instruction, the control unit of the CPU retrieves it from main memory and places it onto a register. The typical operations that take place in the processing of instruction are part of the instruction cycle or execution cycle. The instruction cycle refers to the retrieval of the instruction from main memory and its subsequence at decoding. The process of alerting the circuits in CPU to perform the specified operation. The time it takes to go through the instruction cycle is referred to as I-time.



The output unit of a computer provides the information and results of a computation to outside world. Printers, Visual Display Unit (VDU) are the commonly used output devices. Other commonly used output devices are floppy disk drive, hard disk drive, and magnetic tape drive.


Advantages and Disadvantages of ComputerAdvantages and disadvantages of computer can be listed pointwise below.

Advantages of computer

  1. It saves time
  2. Solves vast equations and other mathematical problems
  3. Communicative device
  4. Creation of virtual reality (V.R.)
  5. Helps to earn money in easy steps
  6. Increases efficiency
  7. Can be used for research and other educational purposes
  8. Helps to explore world through the internet
  9. Helps to make phone call, send messages instantly etc.

Disadvantages of computer

  1. Piracy of original contents may harm a decent developer economically
  2. Hacking may cause different physical damages to an organization
  3. Waste of time on extra stuffs (e.g. pornographic materials, games)
  4. User gets fully dependent on machines only
  5. Can cause eye and other health problems
  6. Can decrease privacy of an organization

Application of computer
Computers have affected the life of people in every field. Computers are used in each and every field such as at science and Engineeering,Education and Research,Business and Industries,Entertainment,Banking e.t.c.

Computer in science and Engineering.

Computers are widely used for engineering purpose.

One of the major areas is CAD (Computer Aided Design) that provides creation and modification of images. Some of the fields are −

  • Structural Engineering − requires stress and strain analysis for design of ships, buildings, budgets, airplanes, etc.
  • Industrial Engineering − Computers deal with design, implementation, and improvement of integrated systems of people, materials, and equipment.
  • Architectural Engineering − Computers help in planning towns, designing buildings, determining a range of buildings on a site using both 2D and 3D drawings.

Computer in communication: Computers are extensively used in sending and receiving information. Data communication packages are available which are used to send or receive information. Different communication services such as electronic mail, internet phone, bulletin board system (BBS), chatting, telex, video conferencing, satellite communication are possible due to computers.

Computer in education: In educational institutions, computers are used as a teaching aid, information resources and computing and research tool. The computer also asks questions to the students and also prepares questions banks and test questions. The computer helps in providing a lot of facilities in the education system.

  • The computer provides a tool in the education system known as CBE (Computer Based Education).
  • CBE involves control, delivery, and evaluation of learning.
  • Computer education is rapidly increasing the graph of number of computer students.
  • There are a number of methods in which educational institutions can use a computer to educate the students.
  • It is used to prepare a database about performance of a student and analysis is carried out on this basis.

Computer in Healthcare

Computers have become an important part in hospitals, labs, and dispensaries. They are being used in hospitals to keep the record of patients and medicines. It is also used in scanning and diagnosing different diseases. ECG, EEG, ultrasounds and CT scans, etc. are also done by computerized machines.

Following are some major fields of health care in which computers are used.

  • Diagnostic System − Computers are used to collect data and identify the cause of illness.
  • Lab-diagnostic System − All tests can be done and the reports are prepared by computer.
  • Patient Monitoring System − these are used to check the patient's signs for abnormality such as in Cardiac Arrest, ECG, etc.
  • Pharma Information System − Computer is used to check drug labels, expiry dates, harmful side effects, etc.
  • Surgery − Nowadays, computers are also used in performing surgery.


Computer in Business

A computer has high speed of calculation, diligence, accuracy, reliability, or versatility which has made it an integrated part in all business organizations.

Computer is used in business organizations for −

  • Payroll calculations
  • Budgeting
  • Sales analysis
  • Financial forecasting
  • Managing employee database
  • Maintenance of stocks, etc.

Computers in banks: Banks use computers for many purposes like to maintain ledger, to provide online services to customers who want to perform bank transaction from home. Computer allows customers to make withdrawals via Automated Telling Machine (ATM). With the use of computer electronic transfer of funds from one account to another has become possible. Banks provide the following facilities −

  • Online accounting facility, which includes checking current balance, making deposits and overdrafts, checking interest charges, shares, and trustee records.
  • ATM machines which are completely automated are making it even easier for customers to deal with banks.

History of Computer 
As the civilization started and they feel the need to count large number and remember them for a long time people felt the need of calculating devices for that they had used to draw lines on the ground in order to find out the quantity. As a result, during the fifth century, the Hindu philosophers developed a new method of counting system using numeric digits from 0 to 9, which is called decimal numeric system.

Mechanical calculating Era


ABACUS: It was derived from the Latin word ABAX. An ABAX is a flat piece of material that is covered with sand. Abacus was one of the first mechanical aids used for calculation created by Chinese 3000 years ago.
Napier’s bone: It was invented by John Napier in 1617 AD. In 1614 he published the first table of logarithm in the book called Rabdologia which was much helpful in simplifying the multiplication of large numbers. In 1617, he invented a small instrument constructed of ten rods called Napier’s bone which were multiplication table inscribed on strips of wood or bone.


Slide rule: In 1620 AD, slide rule was discovered by William Oughtred, an English mathematician of the UK which is an analog device. It was used by engineers for multiplication and division.

Blaise PASCAL: In 1642 AD, a French scientist Blaise Pascal invented a first true mechanical calculating device called Pascaline. Pascaline consist of toothed wheels or gears with each wheel or gear having digits 0 to 9 engraved on it. The machine had capacity to add, subtract 8-bit number. He had invented this machine to assist his father Ethinne Pascal who was a tax superintendent of ROYAN.

Leibniz Calculating Machine: In 1671 a German mathematician Gottfried Wilhem Von Leibniz invented a calculating machine called Leibniz calculating Machine. The stepped Reckoner could perform addition, subtraction, multiplication and division. Leibniz was the first to advocate the use of the binary number system which is fundamental to the operation of modern computers. Leibniz is considered one of the greatest of the philosophers but he died poor and alone.

Jacquard’s loom: Jacquard’s loom’s technology was a real advantage to mill owners, but put many loom operators out of work. Angry loom operators damaged Jacquard’s looms and once attacked Jacquard’s himself.

Electro mechanical era

Mark – I: It was the first electromechanical computer i.e. combination of electrical and mechanical technology. Output was by card punch and electric typewriter. It was slow requiring 3 to 5 seconds for a multiplication, but it was fully automatic and could complete long computations without human intervention.
Atnasoff Berry Computer (ABC): John Vincent Atnasoff, professor of mathematics and physics of Jowa state collage, with the help of his graduate student Clifford Berry, invented ABC computer in 1937 AD. It was the first electronic special purpose computer.


Electronic computer Era

ENIAC (Electronic Numerical and Integrated Calculator): In 1946, John William Mauchly and Jeorge (J) Persper Eckert at the Moore School of Electrical engineering of university of Pennsylvania constructed an ENIAC. It was developed for military needs. It consists of 18000 vacuum tubes, 300 times faster that any other devices invented at that times. It could add two numbers in 200 microseconds and multiply them in 2000 microseconds.
John Von Neumann: Von Neumann contributed a new understanding of how practical fast computers should be organized and built; these ideas, often referred to as the stored – program techniques became fundamental for future generations of high-speed digital computers and were universally adopted. In 1945 he purposed,

  1. A stored program techniques inside the computer
  2. Binary number to be used in computer

EDSAC (Electronic Delay Storage Automatic Computer): It was invented by Murice Wilkes at Cambridge University in 1949. In EDSAC, addition operations took 1500 microseconds and multiplication operation took 4000 microseconds.

EDVAC (Electronic Discrete Variable Automatic Computer): In 1952, John Maunchly and JP Eckert and John Von Neumann invented EDVAC. It used 4000 Vacuum Tubes and 10000 crystal diodes. The EDVAC used the stored program concept in its design.

UNIVAC (Universal Automatic Computer): It was the first general purpose electronic computer designed for commercial use. UNIVAC was the first digital computer that was not of a kind. UNIVAC marked the arrival of commercially available digital computers for business and for scientific applications.

Generations of computer

Each generation of computer is characterized by the major technological development that fundamentally changed the way computer operate, resulting in increasingly smaller, cheaper and more powerful and more efficient and reliable devices. There are totally five generations known till today.

The computers of electronic age are further divided into 5 generation on the basis of technology used by the computer. The different generations are:

                   i) First Generation of computers

                  ii) Second generation of computers

                 iii) Third generation of computers

                 iv) Fourth generation of computers

                v) Fifth generation of computers

i) First Generation of Computers (1945-1954)

1) Technology used: Vacuum tube
2) Operating speed: Millisecond range
3) Programming language used: Machine language
4) Memory used
: Primary memory: Magnetic core memory
: Secondary memory: Magnetic drum, Magnetic tape.
5) I/O device:
Punched card as input device, printing device as output device.
6) Use: Simple mathematical calculation.
7) Computers were extremely large in size, and they required special cooling system. e.g.: ENIVAC, EDVAC, UNIVAC, etc.


  1. They were the fastest calculating devices invented at that time.
  2. Storage capacity was too small (1 to 4 K)
  3. They were very huge in size

Defects of the first generations

  1. There computers were difficult to program and use
  2. Vacuum tubes used to get very hot while using
  3. Difficult to link program


ii) Second generation (1955-1964): These were the first computer that stored their instructions in their memory which moved from magnetic drum to magnetic core technology.


     1) Technology used: Transistor

     2) Operation speed: Micro second range (10-6 sec)

     3) Programming language used: Assembly language

     4) Memory used

           : Primary memory: Magnetic core memory.

           : Secondary memory: Magnetic drum, Magnetic tape.

     5) I/O: Punched card as input device, Printer as output device

     6) Use: Computers were used for complex scientific calculations.

     7) The size, cost, power requirement, heat generation decreased compared to previous generation.

     8) Processing speed, storage capacity, use of the computer increased compared to previous generation.

E.g.: IBM 1620, IBM 7094, LEO MARK III, etc.

Advantages of transistor over vacuum tube:

   i) One transistor could replace one thousand vacuum tubes.

  ii) Size of a transistor is 1/200 th times of a vacuum tube.

 iii) The power requirement of a transistor is 1/20 th times of a vacuum tube.

 iv) Transistors are more reliable than vacuum tube.


Third generation (1964-1975): The development of the integrated circuit (IC) was the hallmark of the third generation computers. Transistors were miniaturized and placed on silicon chips called semiconductors which drastically increased the speed and efficiency of computers.


i) Technology used: IC (Integrated Circuit)

ii) Operating speed: Nanosecond range (10 -9 sec)

iii) Programming language used: HLL (High Level Language)

                            Like FORTAN, COBOL, PASCAL, C, C++, etc.

iv) Memory used:

           Primary memory: Semiconductor memory (silicon)

          Secondary memory: Magnetic tape, Magnetic disk like floppy disk, hard disk, etc)

v) I/O device: Keyboard as input device, monitor as output device.

vi) Use: Computers were used for managing population census, bank, insurance company, etc.

vii) Concept of database was developed and used.

viii) Size, cost, power requirement, heat generation decreased compared to previous generations.

ix) Processing speed, storage capacity, use of the computer increased compared to previous generations.

E.g.: IBM 360 series, ICL 900 series, Honeywell 200 series, etc.


  1. Integrated circuits as main features
  2. Much powerful than second generation computers
  3. They consumed less power
  4. Supported different high level language
  5. Semi-conductors memory was used as primary storage

Fourth generation computers (1975-1989): The microprocessor bought the fourth generation of computers as thousands of integrated circuits were built on to a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand.

       1) Technology used:- VLSI (or Microprocessor)

         2) Operating speed:- Pico second range

         3) Programming language used: 4GL (Problem Oriented Language)

         4) Memory used:

                  Primary: Semi-conductor memory

                  Secondary: Magnetic tape, Magnetic Disk, Optical memory  (CD/DVD/ Blu ray),       Flash  memory(pen drive, memory card)

        5) I/O device:

               Advanced I/O devices like mouse, touch screen, scanner, LCD, LED, color printer, etc are developed.

     6) Use:               Computers are used for different task in different areas like education, business, hospital, transportation, military, etc.

7) Microcomputers like desktop PC, laptop, notebook, etc, are developed.

8) The popular communication media like internet, email, mobile communication, etc were developed.

9) Advanced, user friendly, web based software, etc are developed.

10) Size, cost, power requirement, heat generation decreased compared to previous generation.

11) Operating speed, storage capacity, use of the computer increased compared to previous generation.

E.g.: IBM desktop PC, HP laptop, Acer notebook, Mac book, etc.


  1. Smaller and cheaper
  2. Could understand billions of instructions within a second
  3. General purpose machines
  4. They had faster and larger primary memory and secondary storage devices
  5. Use of the standard high-level languages


Fifth generation (1989-present): The fifth generation of computers are based on artificial intelligence are still under development though there are some application such as voice recognition that are being used today. The use of parallel processing and semiconductors is helping to make artificial intelligence a reality. A computer which will have a brain of own which can make decisions without taking any commands from user is still under construction up to now, hope we shall get it on our local market very soon.
1) Technology to be used:- Bio-chip

2) Operating speed:- Femto second range

(10 -15 second) / TIPS

3) Programming language to be used:- Natural language

4) The computers will have AI.

5) The computers will be used in complex calculation where intelligence of the computer is required.

6) The computers will have parallel processing in full fledge.

7) The computers will be based on KIPS (Knowledge based Information Processing System)


  1. Understands natural language and thinking
  2. They have faster and larger primary memory
  3. They have Gallium arsenide in microprocessor
  4. They are general purpose computers
  5. They have faster and larger primary and secondary storage as compared to their predecessors.

What do you mean by generation of computer?
Originally, the term ‘generation’ was used to distinguish between varying hardware technologies but it has now been extended to include both hardware and software that together make up a computer system. 
Difference between Control unit and ALU

Control unit


1. The CU provides the necessary timing and control signals.

1. ALU is the area of the computer where various computing functions are performed on the data.

2. The unit is responsible for the sequencing jobs of computer (synchronization).

2. All the arithmetic and logical calculations are performed by ALU.

Shortcut to remember:






4th Generation

5th Generation

Technology Used

Vaccum Tube




Bio Chip

Operating Speed






Programming Language

Manching Level

Assembly Level

High Level



Primary Memory

Magnetic Core

Magnetic Core

Magnetic tape, Magnetic disk

Magnetic and Optical disk


Secondary Memory

Magnetic tape, Magnetic drum

Magnetic tape, Magnetic drum

Magnetic tape, Magnetic disk

Magnetic tape, Magnetic disk

Input Device

Punched card

Punched card


Advanced I/O like Mouse,scanner

Output Devics

Printing Device

Printing Device


Advanced I/O like LCD, LED, Color Printer


Very High



Very Low


Very less











Classifications of computers:

 Computers are classified on the basis of their work, size, brand and model.

Classification of computers on the basis of Application

Analog computer: It is a computer or computational device in which the problem variables are represented as continuous varying physical quantities such as temperature and pressure.

Digital computer: A digital computer is an electronic computing machine that uses the binary digits (bits) 0 and 1 to represent all forms of information internally in digital form.

Hybrid computer: Hybrid computers are those computers that contain the features of analog computers and digital computers. A combination of computers is capable of inputting and outputting in both digital and analog signals, e.g. FMC, EICS etc.

Classification of computer on the basis of size

Super computer: Super computer are the fastest, most expensive and the most powerful computers made to process complex and scientific jobs. They are typically used for simulation, animated graphics, weather forecasting, weapon research and development, rocketing and nuclear plasma, physics and meteorology and so on.
Main frame computer: It is a very large and expensive computer capable of supporting hundreds or even thousands of users simultaneously. In the hierarchy that starts with a small microprocessor (in watches for example) at the bottom and moves to supercomputers at the top, mainframes are just below super computers.
Mini computer: A mini computer is a midsized computer. In size and power, mini computers lie between workstation and mainframe computers.
Micro computer: A micro computer is the smallest general purpose processing system based on microprocessor or chip. It consists of CPU in a single chip which supports backing storage of a much smaller scale like hard disk or floppy disk.


Classification of computer on the basis of brand

IBM PC (International Business Machine Personal Computer):

 The computers developed by International Business Machine (IBM) Company are called IBM PCs. The technology used in IBM PC is designed by the engineer of IBM company. IBM PCs are more reliable, durable and have better quality.
IBM compatible: IBM compatible computers are developed by other than IBM companies using the technology of IBM PC. They are easily available.
Apple/Macintosh: Apple computers are developed by Apple Co-operation which was established in late 1970s in the USA. Apple computers are costlier than IBM computers. They are available in different capacity, cost and sizes.


Personal computer: A personal computer is a single user oriented and general purpose micro computer processing system that can execute the program instruction to perform a wide variety of tasks.

Types of personal computers

Desktop computers: Desktop computers are the single user personal computers that can be placed on a desk and hence called desktop. 
Laptop computer: Laptop computers are portable computers mainly used by the people who need computing resources wherever they go. 
Hand held computer: A hand held computer is a device whose size weight and design are such that it can be sued comfortably by holding in hand. It is also known as palmtop computer because it can be kept on palm and operated. PDAs and mobile devices can be illustrated as example of palmtop computers.

Classification of computer on the basis of model


XT computer (extended technology):

 The computer which uses 8086 pr 8088 microprocessor and having processing speed 4.77 MHz is known as an XT computer.
AT Computer: The computer which uses 80286, 80335, 80486 or 80586 series of microprocessor is known as an AT computer.
PS/2 (Personal System -2): These types of computers came in the market after 1990 manufactured by IBM company. Most of the computers developed after 1990s including laptop computer belong to PS/2 model.


Mobile computing:- is human–computer interaction by which a computer is expected to be transported during normal usage, which allows for transmission of data, voice and video. Mobile computing involves mobile communication, mobile hardware, and mobile software. Communication issues include ad hoc networks and infrastructure networks as well as communication properties, protocols, data formats and concrete technologies. Hardware includes mobile devices or device components.


1- Increase in Productivity- Mobile devices can be used out in the field of various companies, therefore reducing the time and cost for clients and themselves.

2- Entertainment- Mobile devices can be used for entertainment purposes, for personal and even for presentations to people and clients.

3- Portability- this would be one of the main advantages of mobile computing, you are not restricted to one location in order for you to get jobs done or even access email on the go


  • quality of connectivity- as one of the disadvantages, mobile devices will need either WiFi connectivity or mobile network connectivity such as GPRS, 3G and in some countries even 4G connectivity  that is why this is a disadvantage because if you are not near any of these connections your access to the internet is very limited.
  • security concerns- Mobile VPNs are unsafe to connect to, and also syncing devices might also lead to security concerns. accessing a WiFi network can also be risky because WPA and WEP security can be bypassed easily.
  • Power Consumption- due to the use of batteries in these devices, these do not tend to last long, if in a situation where there is  no source of power for charging then that will certainly be a let down.