What is Computer?

A computer is a programmable electronic device that accepts raw data as input and processes it
with a set of instructions (a program) to produce the result as output. It renders output just after
performing mathematical and logical operations and can save the output for future use. It can
process numerical as well as non-numerical calculations. The term "computer" is derived from
the Latin word "computare" which means to calculate.

A computer is designed to execute applications and provides a variety of solutions through

integrated hardware and software components. It works with the help of programs and represents
the decimal numbers through a string of binary digits. It also has a memory that stores the data,
programs, and result of processing. The components of a computer such as machinery that
includes wires, transistors, circuits, hard disk are called hardware. Whereas, the programs and
data are called software.

It is believed that the Analytical Engine was the first computer which was invented by Charles
Babbage in 1837. It used punch cards as read-only memory. Charles Babbage is also known as
the father of the computer.

The basic parts without which a computer cannot work are as follows:

o Processor: It executes instructions from software and hardware.

o Memory: It is the primary memory for data transfer between the CPU and storage.
o Motherboard: It is the part that connects all other parts or components of a computer.
o Storage Device: It permanently stores the data, e.g., hard drive.
o Input Device: It allows you to communicate with the computer or to input data, e.g., a
keyboard.
o Output Device: It enables you to see the output, e.g., monitor.

Computers are divided into different types based on different criteria. Based on the size, a
computer can be divided into five types:

1. Micro Computer
2. Mini Computer
3. Mainframe Computer
4. Super Computer
5. Workstations
1. Micro Computer:
It is a single-user computer which has less speed and storage capacity than the other types. It
uses a microprocessor as a CPU. The first microcomputer was built with 8-bit microprocessor
chips. The common examples of microcomputers include laptops, desktop computers, personal
digital assistant (PDA), tablets, and smartphones. Microcomputers are generally designed and
developed for general usage like browsing, searching for information, internet, MS Office, social
media, etc.

2. Mini Computer:
Mini-computers are also known as "Midrange Computers." They are not designed for a single.
They are multi-user computers designed to support multiple users simultaneously. So, they are
generally used by small businesses and firms. Individual departments of a company use these
computers for specific purposes. For example, the admission department of a University can use
a Mini-computer for monitoring the admission process.

3. Mainframe Computer:
It is also a multi-user computer capable of supporting thousands of users simultaneously. They
are used by large firms and government organizations to run their business operations as they can
store and process large amounts of data. For example, Banks, universities, and insurance
companies use mainframe computers to store the data of their customers, students, and
policyholders, respectively.

4. Super Computer:
Super-computers are the fastest and most expensive computers among all types of computers.
They have huge storage capacities and computing speeds and thus can perform millions of
instructions per second. The super-computers are task-specific and thus used for specialized
applications such as large-scale numerical problems in scientific and engineering disciplines
including applications in electronics, petroleum engineering, weather forecasting, medicine,
space research and more. For example, NASA uses supercomputers for launching space satellites
and monitoring and controlling them for space exploration.

5. Work stations:
It is a single-user computer. Although it is like a personal computer, it has a more powerful
microprocessor and a higher-quality monitor than a microcomputer. In terms of storage capacity
and speed, it comes between a personal computer and minicomputer. Work stations are generally
used for specialized applications such as desktop publishing, software development, and
engineering designs.
Benefits of Using a Computer:
o Increases your productivity: A computer increases your productivity. For example,
after having a basic understanding of a word processor, you can create, edit, store, and
print the documents easily and quickly.
o Connects to the Internet: It connects you to the internet that allows you to send emails,
browse content, gain information, use social media platforms, and more. By connecting
to the internet, you can also connect to your long-distance friends and family members.
o Storage: A computer allows you to store a large amount of information, e.g., you can
store your projects, ebooks, documents, movies, pictures, songs, and more.
o Organized Data and Information: It not only allows you to store data but also enables
you to organize your data. For example, you can create different folders to store different
data and information and thus can search for information easily and quickly.
o Improves your abilities: It helps write good English if you are not good at spelling and
grammar. Similarly, if you are not good at math, and don't have a great memory, you can
use a computer to perform calculations and store the results.
o Assist the physically challenged: It can be used to help the physically challenged, e.g.,
Stephen Hawking, who was not able to speak used computer to speak. It also can be used
to help blind people by installing special software to read what is on the screen.
o Keeps you entertained: You can use the computer to listen to songs, watch movies, play
games and more.

The computer has become a part of our life. There are plenty of things that we do in a day are
dependent on a computer. Some of the common examples are as follows:

1. ATM: While withdrawing cash from an ATM, you are using a computer that enables the
ATM to take instructions and dispense cash accordingly.
2. Digital currency: A computer keeps a record of your transactions and balance in your
account and the money deposited in your account in a bank is stored as a digital record or
digital currency.
3. Trading: Stock markets use computers for day to day trading. There are many advanced
algorithms based on computers that handle trading without involving humans.
4. Smartphone: The smartphone that we use throughout the day for calling, texting,
browsing is itself a computer.
 5. VoIP: All voice over IP communication (VoIP) is handled and done by computers.

History of Computers
The first counting device was used by the primitive people. They used sticks, stones and bones as
counting tools. As human mind and technology improved with time more computing devices
were developed. Some of the popular computing devices starting with the first to recent ones are
described below;

Abacus
The history of computer begins with the birth of abacus which is believed to be the first
computer. It is said that Chinese invented Abacus around 4,000 years ago.

It was a wooden rack which has metal rods with beads mounted on them. The beads were moved
by the abacus operator according to some rules to perform arithmetic calculations. Abacus is still
used in some countries like China, Russia and Japan. An image of this tool is shown below;

Napier's Bones
It was a manually-operated calculating device which was invented by John Napier (1550-1617)
of Merchiston. In this calculating tool, he used 9 different ivory strips or bones marked with
numbers to multiply and divide. So, the tool became known as "Napier's Bones. It was also the
first machine to use the decimal point.
Pascaline
Pascaline is also known as Arithmetic Machine or Adding Machine. It was invented between
1642 and 1644 by a French mathematician-philosopher Biaise Pascal. It is believed that it was
the first mechanical and automatic calculator.

Pascal invented this machine to help his father, a tax accountant. It could only perform addition
and subtraction. It was a wooden box with a series of gears and wheels. When a wheel is rotated
one revolution, it rotates the neighboring wheel. A series of windows is given on the top of the
wheels to read the totals. An image of this tool is shown below;
Stepped Reckoner or Leibnitz wheel
It was developed by a German mathematician-philosopher Gottfried Wilhelm Leibnitz in 1673.
He improved Pascal's invention to develop this machine. It was a digital mechanical calculator
which was called the stepped reckoner as instead of gears it was made of fluted drums. See the
following image;

Difference Engine
In the early 1820s, it was designed by Charles Babbage who is known as "Father of Modern
Computer". It was a mechanical computer which could perform simple calculations. It was a
steam driven calculating machine designed to solve tables of numbers like logarithm tables.

Analytical Engine
This calculating machine was also developed by Charles Babbage in 1830. It was a mechanical
computer that used punch-cards as input. It was capable of solving any mathematical problem
and storing information as a permanent memory.
Tabulating Machine
It was invented in 1890, by Herman Hollerith, an American statistician. It was a mechanical
tabulator based on punch cards. It could tabulate statistics and record or sort data or information.
This machine was used in the 1890 U.S. Census. Hollerith also started the Hollerith?s Tabulating
Machine Company which later became International Business Machine (IBM) in 1924.

Differential Analyzer
It was the first electronic computer introduced in the United States in 1930. It was an analog
device invented by Vannevar Bush. This machine has vacuum tubes to switch electrical signals
to perform calculations. It could do 25 calculations in few minutes.
Mark I
The next major changes in the history of computer began in 1937 when Howard Aiken planned
to develop a machine that could perform calculations involving large numbers. In 1944, Mark I
computer was built as a partnership between IBM and Harvard. It was the first programmable
digital computer.

Types of Computer
We can categorize computer in two ways: on the basis of data handling capabilities and size.

On the basis of data handling capabilities, the computer is of three types:

o Analogue Computer
o Digital Computer
o Hybrid Computer

1) Analogue Computer
Analogue computers are designed to process analogue data. Analogue data is continuous data
that changes continuously and cannot have discrete values. We can say that analogue computers
are used where we don't need exact values always such as speed, temperature, pressure and
current.

Analogue computers directly accept the data from the measuring device without first converting
it into numbers and codes. They measure the continuous changes in physical quantity and
generally render output as a reading on a dial or scale. Speedometer and mercury
thermometer are examples of analogue computers.

Advantages of using analogue computers:

o It allows real-time operations and computation at the same time and continuous
representation of all data within the rage of the analogue machine.
o In some applications, it allows performing calculations without taking the help of
transducers for converting the inputs or outputs to digital electronic form and vice versa.
o The programmer can scale the problem for the dynamic range of the analogue computer.
It provides insight into the problem and helps understand the errors and their effects.

Types of analogue computers:

o Slide Rules: It is one of the simplest types of mechanical analogue computers. It was
developed to perform basic mathematical calculations. It is made of two rods. To
perform the calculation, the hashed rod is slid to line up with the markings on another
rod.
o Differential Analysers: It was developed to perform differential calculations. It
performs integration using wheel-and-disc mechanisms to solve differential calculations.
o Castle Clock: It was invented by Al-Jarazi. It was able to save programming
instructions. Its height was around 11 feet and it was provided with the display of time,
the zodiac, and the solar and lunar orbits. This device also could allow users to set the
length of the day as per the current season.
o Electronic Analogue Computer: In this type of analogue computer, electrical signals
flow through capacitors and resistors to simulate physical phenomena. Here, the
mechanical interaction of components does not take place. The voltage of the electrical
signal generates the appropriate displays.

2) Digital Computer
Digital computer is designed to perform calculations and logical operations at high speed. It
accepts the raw data as input in the form of digits or binary numbers (0 and 1) and processes it
with programs stored in its memory to produce the output. All modern computers like laptops,
desktops including smartphones that we use at home or office are digital computers.

Advantages of digital computers:

 o It allows you to store a large amount of information and to retrieve it easily whenever you
need it.
o You can easily add new features to digital systems more easily.
o Different applications can be used in digital systems just by changing the program
without making any changes in hardware
o The cost of hardware is less due to the advancement in the IC technology.
o It offers high speed as the data is processed digitally.
o It is highly reliable as it uses error correction codes.
o Reproducibility of results is higher as the output is not affected by noise, temperature,
humidity, and other properties of its components.

3) Hybrid Computer
Hybrid computer has features of both analogue and digital computer. It is fast like an
analogue computer and has memory and accuracy like digital computers. It can process both
continuous and discrete data. It accepts analogue signals and convert them into digital form
before processing. So, it is widely used in specialized applications where both analogue and
digital data is processed. For example, a processor is used in petrol pumps that converts the
measurements of fuel flow into quantity and price. Similarly, they are used in airplanes,
hospitals, and scientific applications.

Advantages of using hybrid computers:

o Its computing speed is very high due to the all-parallel configuration of the analogue
subsystem.
o It produces precise and quick results that are more accurate and useful.
o It has the ability to solve and manage big equation in real-time.
o It helps in the on-line data processing.

On the basis of size, the computer can be of five types:

1) Supercomputer
Supercomputers are the biggest and fastest computers. They are designed to process huge
amount of data. A supercomputer can process trillions of instructions in a second. It has
thousands of interconnected processors.
Supercomputers are particularly used in scientific and engineering applications such as weather
forecasting, scientific simulations and nuclear energy research. The first supercomputer was
developed by Roger Cray in 1976.

Characteristics or applications of supercomputers:

o It has the ability to decrypt your password to enhance protection for security reasons.
o It produces excellent results in animations.
o It is used for virtual testing of nuclear weapons and critical medical tests.
o It can study and understand climate patterns and forecast weather conditions. It can run in
NOAA's system (National Oceanic and Atmospheric Administration) that can execute
any type of simple and logical data.
o It helps in designing the flight simulators for pilots at the beginner level for their training.
o It helps in extracting useful information from data storage centres or cloud system. For
example, in insurance companies.
o It has played a vital role in managing the online currency world such as stock market and
bitcoin.
o It helps in the diagnosis of various critical diseases and in producing accurate results in
brain injuries, strokes, etc.
o It helps in scientific research areas by accurately analysing data obtained from exploring
the solar system, satellites, and movement of Earth.
o It also used in a smog control system where it predicts the level of fog and other
pollutants in the atmosphere.

2) Mainframe computer
Mainframe computers are designed to support hundreds or thousands of users simultaneously.
They can support multiple programs at the same time. It means they can execute different
processes simultaneously. These features of mainframe computers make them ideal for big
organizations like banking and telecom sectors, which need to manage and process high volume
of data.

Mainframe computers are designed to support hundreds or thousands of users simultaneously.

They can support multiple programs at the same time. It means they can execute different
processes simultaneously. These features of mainframe computers make them ideal for big
organizations like banking and telecom sectors, which need to manage and process a high
volume of data that requires integer operations such as indexing, comparisons, etc.
Characteristics of Mainframe Computers:

o It can process huge amount of data, e.g. millions of transactions in a second in the
banking sector.
o It has a very long life. It can run smoothly for up to 50 years after proper installation.
o It gives excellent performance with large scale memory management.
o It has the ability to share or distribute its workload among other processors and
input/output terminals.
o There are fewer chances of error or bugs during processing in mainframe computers. If
any error occurs it can fix it quickly without affecting the performance.
o It has the ability to protect the stored data and other ongoing exchange of information and
data.

Applications of mainframe computers:

o In health care, it enabled hospitals to maintain a record of their millions of patients in

order to contact them for treatment or related to their appointment, medicine updates or
disease updates.
o In the field of defence, it allows the defence departments to share a large amount of
sensitive information with other branches of defence.
o In the field of education, it helps big universities to store, manage and retrieve data
related to their courses, admissions, students, teachers, employees and affiliated schools
and colleges.
o In the retail sector, the retail companies that have a huge customer base and branches use
mainframe computers to handle and execute information related to their inventory
management, customer management, and huge transactions in a short duration.

3) Miniframe or Minicomputer
It is a midsize multiprocessing computer. It consists of two or more processors and can
support 4 to 200 users at one time. Miniframe computers are used in institutes and departments
for tasks such as billing, accounting and inventory management. A minicomputer lies between
the mainframe and microcomputer as it is smaller than mainframe but larger than a
microcomputer.

Characteristics of miniframe or minicomputer:

 o It is light weight that makes it easy to carry and fit anywhere.
o It is less expensive than mainframe computers.
o It is very fast compared to its size.
o It remains charged for a long time.
o It does not require a controlled operational environment.

Applications of minicomputers:

A minicomputer is mainly used to perform three primary functions, which are as follows:

o Process control: It was used for process control in manufacturing. It mainly performs
two primary functions that are collecting data and feedback. If any abnormality occurs in
the process, it is detected by the minicomputer and necessary adjustments are made
accordingly.
o Data management: It is an excellent device for small organizations to collect, store and
share data. Local hospitals and hotels can use it to maintain the records of their patients
and customers respectively.
o Communications Portal: It can also play the role of a communication device in larger
systems by serving as a portal between a human operator and a central processor or
computer.

4) Workstation
Workstation is a single user computer that is designed for technical or scientific applications. It
has a faster microprocessor, a large amount of RAM and high speed graphic adapters. It
generally performs a specific job with great expertise; accordingly, they are of different types
such as graphics workstation, music workstation and engineering design workstation.

Characteristics of workstation computer:

o It is a high-performance computer system designed for a single user for business or

professional use.
o It has larger storage capacity, better graphics, and more powerful CPU than a personal
computer.
o It can handle animation, data analysis, CAD, audio and video creation and editing.
Any computer that has the following five features, can be termed as a workstation or can be used
as a workstation.

o Multiple Processor Cores: It has more processor cores than simple laptops or
computers.
o ECC RAM: It is provided with Error-correcting code memory that can fix memory
errors before they affect the system's performance.
o RAID (Redundant Array of Independent Disks): It refers to multiple internal hard
drives to store or process data. RAID can be of different types, for example, there can be
multiple drives to process data or mirrored drives where if one drive does not work than
other starts functioning.
o SSD: It is better than conventional hard-disk drives. It does not have moving parts, so the
chances of physical failure are very less.
o Optimized, Higher end GPU: It reduces the load on CPU. E.g., CPU has to do less work
while processing the screen output.

5) Microcomputer
Microcomputer is also known as a personal computer. It is a general-purpose computer that is
designed for individual use. It has a microprocessor as a central processing unit, memory, storage
area, input unit and output unit. Laptops and desktop computers are examples of
microcomputers. They are suitable for personal work that may be making an assignment,
watching a movie, or at office for office work.

Characteristics of a microcomputer:

o It is the smallest in size among all types of computers.

o A limited number of software can be used.
o It is designed for personal work and applications. Only one user can work at a time.
o It is less expansive and easy to use.
o It does not require the user to have special skills or training to use it.
o Generally, comes with single semiconductor chip.
o It is capable of multitasking such as printing, scanning, browsing, watching videos, etc.
Component of Computer
There are 5 main computer components that are given below:

o Input Devices
o CPU
o Output Devices
o Primary Memory
o Secondary Memory

The operations of computer components are given below:

1) Inputting: It is the process of entering raw data, instructions and information into the
computer. It is performed with the help of input devices.

2) Storing: The computer has primary memory and secondary storage to store data and
instructions. It stores the data before sending it to CPU for processing and also stores the
processed data before displaying it as output.

3) Processing: It is the process of converting the raw data into useful information. This process
is performed by the CPU of the computer. It takes the raw data from storage, processes it and
then sends back the processed data to storage.

4) Outputting: It is the process of presenting the processed data through output devices like
monitor, printer and speakers.
5) Controlling: This operation is performed by the control unit that is part of CPU. The control
unit ensures that all basic operations are executed in a right manner and sequence.

Generations of Computers
A generation of computers refers to the specific improvements in computer technology with
time. In 1946, electronic pathways called circuits were developed to perform the counting. It
replaced the gears and other mechanical parts used for counting in previous computing machines.
In each new generation, the circuits became smaller and more advanced than the previous
generation circuits. The miniaturization helped increase the speed, memory and power of
computers. There are five generations of computers which are described below;
First Generation Computers
The first generation (1946-1959) computers were slow, huge and expensive. In these computers,
vacuum tubes were used as the basic components of CPU and memory. These computers were
mainly depended on batch operating system and punch cards. Magnetic tape and paper tape were
used as output and input devices in this generation;
Some of the popular first generation computers are;
o ENIAC ( Electronic Numerical Integrator and Computer)
o EDVAC ( Electronic Discrete Variable Automatic Computer)
o UNIVACI( Universal Automatic Computer)
o IBM-701
o IBM-650
Second Generation Computers
The second generation (1959-1965) was the era of the transistor computers. These computers
used transistors which were cheap, compact and consuming less power; it made transistor
computers faster than the first generation computers.
In this generation, magnetic cores were used as the primary memory and magnetic disc and tapes
were used as the secondary storage. Assembly language and programming languages like
COBOL and FORTRAN, and Batch processing and multiprogramming operating systems were
used in these computers.
Some of the popular second generation computers are;
o IBM 1620
o IBM 7094
o CDC 1604
o CDC 3600
o UNIVAC 1108
Third Generation Computers
The third generation computers used integrated circuits (ICs) instead of transistors. A single IC
can pack huge number of transistors which increased the power of a computer and reduced the
cost. The computers also became more reliable, efficient and smaller in size. These generation
computers used remote processing, time-sharing, multi programming as operating system. Also,
the high-level programming languages like FORTRON-II TO IV, COBOL, PASCAL PL/1,
ALGOL-68 were used in this generation.
Some of the popular third generation computers are;
o IBM-360 series
o Honeywell-6000 series
o PDP(Personal Data Processor)
o IBM-370/168
o TDC-316
Fourth Generation Computers
The fourth generation (1971-1980) computers used very large scale integrated (VLSI) circuits; a
chip containing millions of transistors and other circuit elements. These chips made this
generation computers more compact, powerful, fast and affordable. These generation computers
used real time, time sharing and distributed operating system. The programming languages like
C, C++, DBASE were also used in this generation.
Some of the popular fourth generation computers are;
o DEC 10
o STAR 1000
o PDP 11
o CRAY-1(Super Computer)
o CRAY-X-MP(Super Computer)
Fifth Generation Computers
In fifth generation (1980-till date) computers, the VLSI technology was replaced with ULSI
(Ultra Large Scale Integration). It made possible the production of microprocessor chips with ten
million electronic components. This generation computers used parallel processing hardware and
AI (Artificial Intelligence) software. The programming languages used in this generation were C,
C++, Java, .Net, etc.
Some of the popular fifth generation computers are;
o Desktop
o Laptop
o NoteBook
o UltraBook
o ChromeBook

Number System
When we type some letters or words, the computer translates them in numbers as computers can
understand only numbers. A computer can understand the positional number system where there
are only a few symbols called digits and these symbols represent different values depending on
the position they occupy in the number.
The value of each digit in a number can be determined using −
 The digit
 The position of the digit in the number
 The base of the number system (where the base is defined as the total number of digits
available in the number system)
Decimal Number System
The number system that we use in our day-to-day life is the decimal number system. Decimal
number system has base 10 as it uses 10 digits from 0 to 9. In decimal number system, the
successive positions to the left of the decimal point represent units, tens, hundreds, thousands,
and so on.
Each position represents a specific power of the base (10). For example, the decimal number
1234 consists of the digit 4 in the units position, 3 in the tens position, 2 in the hundreds position,
and 1 in the thousands position. Its value can be written as
(1 x 1000)+ (2 x 100)+ (3 x 10)+ (4 x l)
(1 x 103)+ (2 x 102)+ (3 x 101)+ (4 x l00)
1000 + 200 + 30 + 4
1234
As a computer programmer or an IT professional, you should understand the following number
systems which are frequently used in computers.
S.No. Number System and Description

1 Binary Number System

Base 2. Digits used : 0, 1

2 Octal Number System

Base 8. Digits used : 0 to 7

3 Hexa Decimal Number System

Base 16. Digits used: 0 to 9, Letters used : A- F

Binary Number System

Characteristics of the binary number system are as follows −
 Uses two digits, 0 and 1
 Also called as base 2 number system
 Each position in a binary number represents a 0 power of the base (2). Example 20
 Last position in a binary number represents a x power of the base (2). Example
2x where x represents the last position - 1.

Example
Binary Number: 101012
Calculating Decimal Equivalent −
Step Binary Number Decimal Number
Step 1 101012 ((1 x 24) + (0 x 23) + (1 x 22) + (0 x 21) + (1 x 20))10

Step 2 101012 (16 + 0 + 4 + 0 + 1)10

Step 3 101012 2110

Note − 101012 is normally written as 10101.
Octal Number System
Characteristics of the octal number system are as follows −
 Uses eight digits, 0,1,2,3,4,5,6,7
 Also called as base 8 number system
 Each position in an octal number represents a 0 power of the base (8). Example 80
 Last position in an octal number represents a x power of the base (8). Example
8x where x represents the last position - 1

Example
Octal Number: 125708
Calculating Decimal Equivalent −
Step Octal Number Decimal Number

Step 1 125708 ((1 x 84) + (2 x 83) + (5 x 82) + (7 x 81) + (0 x 80))10

Step 2 125708 (4096 + 1024 + 320 + 56 + 0)10

Step 3 125708 549610

Note − 125708 is normally written as 12570.
Hexadecimal Number System
Characteristics of hexadecimal number system are as follows −
 Uses 10 digits and 6 letters, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
 Letters represent the numbers starting from 10. A = 10. B = 11, C = 12, D = 13, E = 14, F
= 15
 Also called as base 16 number system
 Each position in a hexadecimal number represents a 0 power of the base (16). Example,
160
 Last position in a hexadecimal number represents a x power of the base (16). Example
16x where x represents the last position - 1

Example
Hexadecimal Number: 19FDE16
Calculating Decimal Equivalent −
Step Binary Decimal Number
 Number

Step 1 19FDE16 ((1 x 164) + (9 x 163) + (F x 162) + (D x 161) + (E x 160))10

Step 2 19FDE16 ((1 x 164) + (9 x 163) + (15 x 162) + (13 x 161) + (14 x 160))10

Step 3 19FDE16 (65536+ 36864 + 3840 + 208 + 14)10

Step 4 19FDE16 10646210

Note − 19FDE16 is normally written as 19FDE.

ASCII - Binary Character Table

Letter ASCII Code Binary Letter ASCII Code Binary

a 097 01100001 A 065 01000001
b 098 01100010 B 066 01000010
c 099 01100011 C 067 01000011
d 100 01100100 D 068 01000100
e 101 01100101 E 069 01000101
f 102 01100110 F 070 01000110
g 103 01100111 G 071 01000111
h 104 01101000 H 072 01001000
i 105 01101001 I 073 01001001
j 106 01101010 J 074 01001010
k 107 01101011 K 075 01001011
l 108 01101100 L 076 01001100
m 109 01101101 M 077 01001101
n 110 01101110 N 078 01001110
o 111 01101111 O 079 01001111
p 112 01110000 P 080 01010000
q 113 01110001 Q 081 01010001
r 114 01110010 R 082 01010010
s 115 01110011 S 083 01010011
t 116 01110100 T 084 01010100
u 117 01110101 U 085 01010101
 v 118 01110110 V 086 01010110
w 119 01110111 W 087 01010111
x 120 01111000 X 088 01011000
y 121 01111001 Y 089 01011001
z 122 01111010 Z 090 01011010

Block Diagram of Computer

There are 5 main computer components that are given below:

o Input Devices
o CPU
o Output Devices
o Primary Memory
o Secondary Memory

The operations of computer components are given below:

1) Inputting: It is the process of entering raw data, instructions and information into the
computer. It is performed with the help of input devices.
2) Storing: The computer has primary memory and secondary storage to store data and
instructions. It stores the data before sending it to CPU for processing and also stores the
processed data before displaying it as output.

3) Processing: It is the process of converting the raw data into useful information. This process
is performed by the CPU of the computer. It takes the raw data from storage, processes it and
then sends back the processed data to storage.

4) Outputting: It is the process of presenting the processed data through output devices like
monitor, printer and speakers.

5) Controlling: This operation is performed by the control unit that is part of CPU. The control
unit ensures that all basic operations are executed in a right manner and sequence.

Input Devices
Input device enables the user to send data, information, or control signals to a computer. The
Central Processing Unit (CPU) of a computer receives the input and processes it to produce the
output.

Some of the popular input devices are:

1. Keyboard
2. Mouse
3. Scanner
4. Joystick
5. Light Pen
6. Digitizer
7. Microphone
8. Magnetic Ink Character Recognition (MICR)
9. Optical Character Reader (OCR)
10. Digital Camera
11. Paddle
12. Steering Wheel
13. Gesture recognition devices
14. Light Gun
15. Touch Pad
 16. Remote
17. Touch screen
18. VR

Output Devices
The output device displays the result of the processing of raw data that is entered in the computer
through an input device. There are a number of output devices that display output in different
ways such as text, images, hard copies, and audio or video.

Some of the popular output devices are:

1. Monitor
o CRT Monitor
o LCD Monitor
o LED Monitor
o Plasma Monitor
2. Printer
o Impact Printers
A. Character Printers
i. Dot Matrix printers
ii. Daisy Wheel printers
B. Line printers
i. Drum printers
ii. Chain printers
o Non-impact printers
A. Laser printers
B. Inkjet printers
3. Projector
Operating System

Operating System Tutorial provides the basic and advanced concepts of operating system . Our
Operating system tutorial is designed for beginners, professionals and GATE aspirants. We have
designed this tutorial after the completion of a deep research about every concept.

The content is described in detailed manner and has the ability to answer most of your queries.
The tutorial also contains the numerical examples based on previous year GATE questions which
will help you to address the problems in a practical manner.

Operating System can be defined as an interface between user and the hardware. It provides an
environment to the user so that, the user can perform its task in convenient and efficient way.

The Operating System Tutorial is divided into various parts based on its functions such as
Process Management, Process Synchronization, Deadlocks and File Management.

Operating System Definition and Function

In the Computer System (comprises of Hardware and software), Hardware can only understand
machine code (in the form of 0 and 1) which doesn't make any sense to a naive user.

We need a system which can act as an intermediary and manage all the processes and resources
present in the system.
An Operating System can be defined as an interface between user and hardware. It is
responsible for the execution of all the processes, Resource Allocation, CPU management, File
Management and many other tasks.

The purpose of an operating system is to provide an environment in which a user can execute
programs in convenient and efficient manner.

Structure of a Computer System

A Computer System consists of:

o Users (people who are using the computer)

o Application Programs (Compilers, Databases, Games, Video player, Browsers, etc.)
o System Programs (Shells, Editors, Compilers, etc.)
o Operating System ( A special program which acts as an interface between user and hardware )
o Hardware ( CPU, Disks, Memory, etc)
What does an Operating system do?
1. Process Management
2. Process Synchronization
3. Memory Management
4. CPU Scheduling
5. File Management
6. Security

Compiler and Interpreter

We mostly write a computer program in high-level languages, which humans understand. High-
level languages are that which contains words and phrases from human languages - for example,
English. The high-level programming language is also known as source code in a computer
program. However, computer machine does not understand these high-level programming
languages. It only understood its machine code, i.e., a program in 0's and 1's in binary form to
perform the task accordingly.

To perform an instruction written in high-level language via computer, we need to convert it into
machine language. To do this, either a compiler or an interpreter, or both are used to convert a
source code programming language into machine code. Compiler and interpreter are software
programs that convert a high-level language into a machine language (0's and 1's binary form)
that a computer can understand and perform tasks as per the program's instructions. But there are
variations in the working process and steps of a compiler and interpreter. Before diving into the
difference between a compiler and an interpreter, let's see a brief introduction about both of
them.

Computer Languages
The user of a computer must be able to communicate with it. That means, he must be able to give
the computer commands and understand the output that the computer generates. This is possible due
to the invention of computer languages.

Basically, there are two main categories of computer languages, namely Low Level Language and
High Level Language. Let us take a brief look at both these types of computer languages.
1] Low Level Languages
Low level languages are the basic computer instructions or better known as machine codes. A
computer cannot understand any instruction given to it by the user in English or any other high level
language. These low level languages are very easily understandable by the machine.

The main function of low level languages is to interact with the hardware of the computer. They
help in operating, syncing and managing all the hardware and system components of the computer.
They handle all the instructions which form the architecture of the hardware systems.

Machine Language
This is one of the most basic low level languages. The language was first developed to interact with
the first generation computers. It is written in binary code or machine code, which means it basically
comprises of only two digits – 1 and 0.

Assembly Language
This is the second generation programming language. It is a development on the machine language,
where instead of using only numbers, we use English words, names, and symbols. It is the most
basic computer language necessary for any processor.

2] High Level Language

When we talk about high level languages, these are programming languages. Some prominent
examples are PASCAL, FORTRAN, C++ etc.

The important feature about such high level languages is that they allow the programmer to write
programs for all types of computers and systems. Every instruction in high level language is
converted to machine language for the computer to comprehend.
Scripting Languages

Scripting languages or scripts are essentially programming languages. These languages employ a
high level construct which allows it to interpret and execute one command at a time.

Scripting languages are easier to learn and execute than compiled languages. Some examples are
AppleScript, JavaScript, Pearl etc.

Object-Oriented Languages

These are high level languages that focus on the ‘objects’ rather than the ‘actions’. To accomplish
this, the focus will be on data than logic.

The reasoning behind is that the programmers really cares about the object they wish to manipulate
rather than the logic needed to manipulate them. Some examples include Java, C+, C++, Python,
Swift etc.

Procedural Programming Language

This is a type of programming language that has well structured steps and complex procedures
within its programming to compose a complete program.

It has a systematic order functions and commands to complete a task or a program. FORTRAN,
ALGOL, BASIC, COBOL are some examples.

Computer Memory
The computer memory holds the data and instructions needed to process raw data and produce
output. The computer memory is divided into large number of small parts known as cells. Each
cell has a unique address which varies from 0 to memory size minus one.

Computer memory is of two types: Volatile (RAM) and Non-volatile (ROM). The secondary
memory (hard disk) is referred as storage not memory.

But, if we categorize memory on behalf of space or location, it is of four types:

o Register memory
o Cache memory
o Primary memory
o Secondary memory
Register Memory
Register memory is the smallest and fastest memory in a computer. It is not a part of the main
memory and is located in the CPU in the form of registers, which are the smallest data holding
elements. A register temporarily holds frequently used data, instructions, and memory address
that are to be used by CPU. They hold instructions that are currently processed by the CPU. All
data is required to pass through registers before it can be processed. So, they are used by CPU to
process the data entered by the users.

Registers hold a small amount of data around 32 bits to 64 bits. The speed of a CPU depends on
the number and size (no. of bits) of registers that are built into the CPU. Registers can be of
different types based on their uses. Some of the widely used Registers include Accumulator or
AC, Data Register or DR, the Address Register or AR, Program Counter (PC), I/O Address
Register, and more.

Types and Functions of Computer Registers:

o Data Register: It is a 16-bit register, which is used to store operands (variables) to be operated by
the processor. It temporarily stores data, which is being transmitted to or received from a
peripheral device.
o Program Counter (PC): It holds the address of the memory location of the next instruction,
which is to be fetched after the current instruction is completed. So, it is used to maintain the path
of execution of the different programs and thus executes the programs one by one, when the
previous instruction gets completed.
o Instructor Register: It is a 16-bit register. It stores the instruction which is fetched from the
main memory. So, it is used to hold instruction codes, which are to be executed. The Control Unit
takes instruction from Instructor Register, then decodes and executes it.
o Accumulator Register: It is a 16-bit register, which is used to store the results produced by the
system. For example, the results generated by CPU after the processing are stored in the AC
register.
o Address Register: It is a 12-bit register that stores the address of a memory location where
instructions or data is stored in the memory.
o I/O Address Register: Its job is to specify the address of a particular I/O device.
o I/O Buffer Register: Its job is to exchange the data between an I/O module and the CPU.
Cache Memory
Cache memory is a high-speed memory, which is small in size but faster than the main memory
(RAM). The CPU can access it more quickly than the primary memory. So, it is used to
synchronize with high-speed CPU and to improve its performance.

Cache memory can only be accessed by CPU. It can be a reserved part of the main memory or a
storage device outside the CPU. It holds the data and programs which are frequently used by the
CPU. So, it makes sure that the data is instantly available for CPU whenever the CPU needs this
data. In other words, if the CPU finds the required data or instructions in the cache memory, it
doesn't need to access the primary memory (RAM). Thus, by acting as a buffer between RAM
and CPU, it speeds up the system performance.

Types of Cache Memory:

L1: It is the first level of cache memory, which is called Level 1 cache or L1 cache. In this type
of cache memory, a small amount of memory is present inside the CPU itself. If a CPU has four
cores (quad core cpu), then each core will have its own level 1 cache. As this memory is present
in the CPU, it can work at the same speed as of the CPU. The size of this memory ranges from
2KB to 64 KB. The L1 cache further has two types of caches: Instruction cache, which stores
instructions required by the CPU, and the data cache that stores the data required by the CPU.
L2: This cache is known as Level 2 cache or L2 cache. This level 2 cache may be inside the
CPU or outside the CPU. All the cores of a CPU can have their own separate level 2 cache, or
they can share one L2 cache among themselves. In case it is outside the CPU, it is connected
with the CPU with a very high-speed bus. The memory size of this cache is in the range of 256
KB to the 512 KB. In terms of speed, they are slower than the L1 cache.

Primary Memory
Primary Memory is of two types: RAM and ROM.

RAM (Volatile Memory)

It is a volatile memory. It means it does not store data or instructions permanently. When you
switch on the computer the data and instructions from the hard disk are stored in RAM.

CPU utilizes this data to perform the required tasks. As soon as you shut down the computer the
RAM loses all the data.

ROM (Non-volatile Memory)

It is a non-volatile memory. It means it does not lose its data or programs that are written on it at
the time of manufacture. So it is a permanent memory that contains all important data and
instructions needed to perform important tasks like the boot process.

Secondary Memory
The secondary storage devices which are built into the computer or connected to the computer
are known as a secondary memory of the computer. It is also known as external memory or
auxiliary storage.

The secondary memory is accessed indirectly via input/output operations. It is non-volatile, so

permanently stores the data even when the computer is turned off or until this data is overwritten
or deleted. The CPU can't directly access the secondary memory. First, the secondary memory
data is transferred to primary memory then the CPU can access it.