Page 22 - DCAP101_BASIC_COMPUTER_SKILLS

Unit 1: Computer Fundamentals

1. Primary Storage: Stores and provides very fast. This memory is generally used to hold Notes
the program being currently executed in the computer, the data being received from
the input unit, the intermediate and final results of the program. The primary memory
is temporary in nature. The data is lost, when the computer is switched off. In order
to store the data permanently, the data has to be transferred to the secondary memory.
The cost of the primary storage is more compared to the secondary storage. Therefore,
most computers have limited primary storage capacity.
2. Secondary Storage: Secondary storage is used like an archive. It stores several programs,
documents, data bases etc. The programs that you run on the computer are first transferred
to the primary memory before it is actually run. Whenever the results are saved, again
they get stored in the secondary memory. The secondary memory is slower and cheaper
than the primary memory. Some of the commonly used secondary memory devices are
Hard disk, CD, etc.
1.4.3 Memory Size

All digital computers use the binary system, i.e. 0’s and 1’s. Each character or a number is
represented by an 8 bit code. The set of 8 bits is called a byte. A character occupies 1 byte space.
A numeric occupies 2 byte space. Byte is the space occupied in the memory. The size of the
primary storage is specified in KB (Kilobytes) or MB (Megabyte). One KB is equal to 1024 bytes
and one MB is equal to 1000 KB. The size of the primary storage in a typical PC usually starts
at 16 MB. PCs having 32 MB, 48 MB, 128 MB, 256 MB memory are quite common.
1.4.4 Output Unit

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.
1.4.5 Arithmetic Logical Unit

All calculations are performed in the Arithmetic Logic Unit (ALU) of the computer. It also
does comparison and takes decision. The ALU can perform basic operations such as addition,
subtraction, multiplication, division, etc and does logic operations viz, >, <, =, ‘etc. Whenever
calculations are required, the control unit transfers the data from storage unit to ALU once
the computations are done, the results are transferred to the storage unit by the control unit
and then it is send to the output unit for displaying results.
1.4.6 Control Unit

It controls all other units in the computer. The control unit instructs the input unit, where
to store the data after receiving it from the user. It controls the flow of data and instructions
from the storage unit to ALU. It also controls the flow of results from the ALU to the storage
unit. The control unit is generally referred as the central nervous system of the computer
that control and synchronizes its working.

1.4.7 Central Processing Unit
The control unit and ALU of the computer are together known as the Central Processing Unit
(CPU). The CPU is like brain performs the following functions:
• It performs all calculations.
• It takes all decisions.

• It controls all units of the computer.

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