CHAPTER 2

Computer Components

All types of computers follow the same basic logical structure and perform the following five
basic operations for converting raw input data into information useful to their users.

S.No. Operation Description

1 Take Input The process of entering data and instructions into the computer system.

2 Store Data Saving data and instructions so that they are available for processing as
and when required.

3 Processing Data Performing arithmetic, and logical operations on data in order to convert
them into useful information.

4 Output The process of producing useful information or results for the user, such
Information as a printed report or visual display.

5 Control the Directs the manner and sequence in which all of the above operations
workflow are performed.

Input Unit

This unit contains devices with the help of which we enter data into the computer. This unit
creates a link between the user and the computer. The input devices translate the information
into a form understandable by the computer.
CPU (Central Processing Unit)

CPU is considered as the brain of the computer. CPU performs all types of data processing
operations. It stores data, intermediate results, and instructions (program). It controls the
operation of all parts of the computer.

CPU itself has the following three components −

 ALU (Arithmetic Logic Unit)

 Memory Unit

 Control Unit

Output Unit

The output unit consists of devices with the help of which we get the information from the
computer. This unit is a link between the computer and the users. Output devices translate the
computer's output into a form understandable by the users.

Components of CPU

Central Processing Unit (CPU) consists of the following features −

 CPU is considered as the brain of the computer.

 CPU performs all types of data processing operations.

 It stores data, intermediate results, and instructions (program).

 It controls the operation of all parts of the computer.

CPU itself has following three components.

 Memory or Storage Unit

 Control Unit

 ALU(Arithmetic Logic Unit)

Memory or Storage Unit

This unit can store instructions, data, and intermediate results. This unit supplies information to
other units of the computer when needed. It is also known as internal storage unit or the main
memory or the primary storage or Random Access Memory (RAM).
Its size affects speed, power, and capability. Primary memory and secondary memory are two
types of memories in the computer. Functions of the memory unit are −

 It stores all the data and the instructions required for processing.
 It stores intermediate results of processing.
 It stores the final results of processing before these results are released to an output
device.
 All inputs and outputs are transmitted through the main memory.

Control Unit

This unit controls the operations of all parts of the computer but does not carry out any actual
data processing operations.

Functions of this unit are −

 It is responsible for controlling the transfer of data and instructions among other units of
a computer.
 It manages and coordinates all the units of the computer.
 It obtains the instructions from the memory, interprets them, and directs the operation of
the computer.
 It communicates with Input/Output devices for transfer of data or results from storage.
 It does not process or store data.

ALU (Arithmetic Logic Unit)

This unit consists of two subsections namely,

 Arithmetic Section

 Logic Section

Arithmetic Section

Function of arithmetic section is to perform arithmetic operations like addition, subtraction,

multiplication, and division. All complex operations are done by making repetitive use of the
above operations.

Logic Section
Function of logic section is to perform logic operations such as comparing, selecting, matching,
and merging of data.

Computer Memory

 A memory is just like a human brain. It is used to store data and instructions. Computer
memory is the storage space in the computer, where data is to be processed and
instructions required for processing are stored.
 The memory is divided into large number of small parts called cells. Each location or
cell has a unique address, which varies from zero to memory size minus one.
 Memory is primarily of three types −

 Cache Memory

 Primary Memory/Main Memory

 Secondary Memory

Cache Memory

 Cache memory is a very high speed semiconductor memory which can speed up the
CPU.
 It acts as a buffer between the CPU and the main memory. It is used to hold those parts
of data and program which are most frequently used by the CPU.
 The parts of data and programs are transferred from the disk to cache memory by the
operating system, from where the CPU can access them.

Advantages

The advantages of cache memory are as follows −

 Cache memory is faster than main memory.

 It consumes less access time as compared to main memory.

 It stores the program that can be executed within a short period of time.

 It stores data for temporary use.

Disadvantages
The disadvantages of cache memory are as follows −

 Cache memory has limited capacity.

 It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which the computer is currently
working. It has a limited capacity and data is lost when power is switched off. It is generally
made up of semiconductor device. These memories are not as fast as registers. The data and
instruction required to be processed resides in the main memory. It is divided into two
subcategories RAM and ROM.

Characteristics of Main Memory

 These are semiconductor memories.

 It is known as the main memory.

 Usually volatile memory.

 Data is lost in case power is switched off.

 It is the working memory of the computer.

 Faster than secondary memories.

 A computer cannot run without the primary memory.

Secondary Memory
This type of memory is also known as external memory or non-volatile. It is slower than the
main memory. These are used for storing data/information permanently. CPU directly does not
access these memories, instead they are accessed via input-output routines. The contents of
secondary memories are first transferred to the main memory, and then the CPU can access it.
For example, disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory

 These are magnetic and optical memories.

 It is known as the backup memory.

  It is a non-volatile memory.

 Data is permanently stored even if power is switched off.

 It is used for storage of data in a computer.

 Computer may run without the secondary memory.

 Slower than primary memories.

Memory Units:

 Memory unit is the amount of data that can be stored in the storage unit. This storage
capacity is expressed in terms of Bytes.
 The following table explains the main memory storage units −

S.No. Unit & Description

1 Bit (Binary Digit)

A binary digit is logical 0 and 1 representing a passive or an active state of a component in

an electric circuit.

2 Nibble

A group of 4 bits is called nibble.

3 Byte

A group of 8 bits is called byte. A byte is the smallest unit, which can represent a data item
or a character.

4 Word

A computer word, like a byte, is a group of fixed number of bits processed as a unit, which
varies from computer to computer but is fixed for each computer.

The length of a computer word is called word-size or word length. It may be as small as 8
bits or may be as long as 96 bits. A computer stores the information in the form of computer
words.

 The following table lists some higher storage units −

S.No. Unit & Description

1 Kilobyte (KB)

1 KB = 1024 Bytes

2 Megabyte (MB)

1 MB = 1024 KB

3 GigaByte (GB)

1 GB = 1024 MB

4 TeraByte (TB)

1 TB = 1024 GB

5 PetaByte (PB)

1 PB = 1024 TB