A computer is a programmable machine that performs arithmetic and logical operations on input provided by the user to produce output. It has hardware components like the CPU and memory that execute instructions, as well as software programs. A computer is fast, accurate, can store large amounts of data, and work diligently for long periods without breaks. It has no intelligence or feelings. An operating system coordinates between the user and hardware and allows programs to run. Common functions of operating systems include task scheduling, memory management, and handling input/output.

2. A computer is a programmable machine designed to
perform arithmetic and logical operations
automatically and sequentially on the input given by
the user and gives the desired output after processing.
Computer components are divided into two major
categories namely hardware and software.
 Hardware is the machine itself and its connected
devices such as monitor, keyboard, mouse etc.
 Software are the set of programs that make use of
hardware for performing various functions.

3. Characteristics of Computer
 SPEED : In general, no human being can compete to solving the
complex computation, faster than computer.
 ACCURACY : Since Computer is programmed, so what ever
input we give it gives result with accurately.
 STORAGE : Computer can store mass storage of data with
appropriate format.
 DILIGENCE : Computer can work carefully for hours without
any break and creating error.
 VERSATILITY : We can use computer to perform completely
different type of work at the same time. Flexibility.
 POWER OF REMEMBERING : It can remember data for us.
 NO IQ : Computer does not work without instruction.
 NO FEELING : Computer does not have emotions, knowledge,
experience, feeling.

4. Computer and its components
 Computer : Computer itself a combination of different type of separate electronic device. i.e. Computer only will be
computer if it has INPUT DEVICE, PROCESS UNIT, and OUTPUT DEVICE.
 Central Processing Unit (CPU) : It is heart and mind of the computer without this unit computer unable to process.
 Keyboard , Mouse , Monitor, LCD : It is known as Liquid Crystal Display. It is an output device as monitor.
 Switch Mode Power Supply (SMPS) , Universal Serial Bus (USB) , Pen Drive , Ethernet Port , CD/DVD ROM , Speaker ,
Mike, Sound Card, Graphics Card
 Hard Disk (HDD) : This is used to store the data in massive amount. There are so many type of HDD available in the
market, i.e. SATA, PATA, External HDD, Internal HDD.
 Printer : This is an out put device which is used to show the result on the paper. There are plenty of printer available in the
market like inkjet, Laser printer, dot matrix printer etc.
 Scanner : This is an input device which is used to scan the document for the soft copy.
 Laptop : This is complete computer which can be carried anywhere any time.
 Notebook : This is called mini laptop which is generally lighter and smaller than laptop.
 Random Access Memory (RAM) : This is called primary memory. This is also called main memory of the computer.
Whatever data is written in this memory, is lost after switching off the system.
 Read Only Memory (ROM) : This is called primary memory. Data is written in this memory by the vendor of the computer
permanently.
 Blue Ray Disk : This is same as CD/DVD but only different is it can store multi time of data from CD/DVD and faster than
CD/DVD.
 Motherboard : It is a combination of electronic circuits.

5. Computer Software
 Computer software is the set of programs that makes the
hardware perform a set of tasks in particular order.
Hardware and software are complimentary to each other.
Both have to work together to produce meaningful results.
Computer software is classified into two broad categories;
system software and application software.
System Software:
 System software consists of a group of programs that
control the operations of a computer equipment including
functions like managing memory, managing peripherals,
loading, storing, and is an interface between the
application programs and the computer. MS DOS
(Microsoft’s Disk Operating System), UNIX are examples of
system software.

6. Computer Software
Application software:
 Software that can perform a specific task for the user, such
as word processing, accounting, budgeting or payroll, fall
under the category of application software. Word
processors, spreadsheets, database management systems
are all examples of general purpose application software.
 Types of application software are:
• Word processing software, Database software (MS access,
FoxPro, Oracle etc.), Spread sheet software, Presentation
software, Multimedia software, Media players and real
players are the examples of multimedia software. This
software will allow the user to create audio and videos. The
different forms of multimedia software are audio
converters, players, burners, video encoders and decoders.

7. Computer Languages
 Machine Level Language : This is low level programming
language. Computer or any electronic device only understand
this language. i.e. Binary number i. e. 0 and 1.
 Assembly Level Language : This is a low level programming
language which is converted into executable machine code by a
utility programmer referred to as an assembler.
 High Level Language : High level language is a programming
language which is easily understandable/readable by human.
 Interpreter : This is a convertor which converts high level
language program to low level language program line by line.
 Compiler : This is also a convertor which converts whole high
level language program to low level language program at a
time.

8. Number System
Binary Number System : It has only base 2
i.e 0 and 1
Octal Number System : Base of octal is 8
i.e. 0, 1, 2, 3, 4, 5, 6, 7
Decimal Number System : Base of
Decimal is 10 i.e. 0 1 2 3 4 5 6 7 8 9
Hexadecimal Number System : Base of
this number system is 16 i.e. 0 1 2 3 4 5 6 7
8 9 A B C D E F

9. Classification of Computers
 Analog Computers: It accepts analog input and provide analog
output information. It represents physical quantities like
acceleration, temperature, distance or voltages in mechanical or
electrical circuits and does not need any storage device. E.g.
thermometer, speedometer and analog clock.
 Digital Computers: This computer accept digital input and
provide digital output after processing information and the
operation are in binary system of 0 and 1. By manipulating the
binary digits and numbers it can perform like analyze data,
mathematical calculation etc.
 Hybrid Computers: This computer is the combination of both
analog and digital computers in term of speed and accuracy.
Hybrid computers can measure physical and digital quantities.
E.g. Heartbeat measurement machine, fuel pumps.

10. Operating System
 An operating system (also called an OS) is a piece of software that is
needed to run the programs on a computer or a mobile device. The
programs that run on an operating system talk to the hardware
(specifically through the BIOS). Microsoft Windows and Mac OS are
common operating systems. Less common, but important operating
systems are Linux, Unix, and Solaris.
 Operating System is a set of control programs which coordinates
between user & hardware and forms an interface between them. It is
also known as "System Software", "Computer System" or
"Executive System".
 It accepts command in simple English language and converts it to
signals or machine language which computer hardware can
understand. Computer Hardware are electronic components which
communicates among themselves in electronics signals for
performing their task. Users of computer does not understand
electronic signals so it is next to impossible for a person to operate
computer without Operating System.

11. Functions of OSThe main functions of an OS include:
In a multitasking operating system where multiple programs can be running at the same time,
the operating system determines which applications should run in what order and how much
time should be allowed for each application before giving another application a turn.
• It manages the sharing of internal memory among multiple applications.
• It handles and monitors input and output to and from attached hardware devices, such as hard
disks, printers, and dial-up ports.
• It sends messages to each application or interactive user (or to a system operator) about the
status of operation and any errors that may have occurred.
• It can offload the management of what are called batch jobs (for example, printing) so that the
initiating application is freed from this work.
• On computers that can provide parallel processing, an operating system can manage how to
divide the program so that it runs on more than one processor at a time.
• Scheduling the activities of the CPU and resources to achieve efficiency and prevention of
deadlock.
Tasks commonly done by operating systems:
Interaction with the user, and management of attached devices (such as USB flash drives)
• Management of programs (things like starting and stopping them)
• Management of resources like processor time: Making sure each program gets to run in turn
• The reading and writing of data
• Memory management: virtual memory, paging, swapping

12. Types of OS
 Batch Processing System: Data or programs are collected
grouped and processed at a later date. E.g. Payroll, stock
control and billing systems
 Real-time Systems: Inputs immediately affect the outputs.
Timing is critical i.e. they are capable of influencing the source
of the data e.g. control where data from sensors is processed
immediately and affect the outputs - controlling some device.
Timing is critical and the term real-time control system. E.g.
control of nuclear power plants, oil refining, chemical
processing and traffic control systems, air.
 Real-time transaction: Inputs immediately affect the outputs
but timing is not critical. Each transaction is completed online
as it arises e.g. booking systems - each booking is online and a
database of bookings can be amended interactively and very
quickly whilst another user is locked out so cannot double book
or alter that record at the same time. E.g. Holiday and airline
booking system