Page 6 - 00inner.cdr

Primary memory can be divided into two parts – RAM and ROM.

1. RAM : RAM stands for Random Access Memory. RAM refers to
read and write memory. Information can be written onto and read
from RAM. RAM is volatile in nature. So, whenever power fails or
the computer is switched off, all the information that has been

stored in RAM is lost. It stores information on a temporary basis.

2. ROM : ROM stands for Read Only Memory. It keeps the data
permanent. It is non-volatile in nature. It retains the data even
when a computer is switched off.

In most computers, ROM is used for storing a special program called BIOS (Basic Input
Output System). This program helps to load the operating system when the computer is
switched on.

There are three different kinds of ROM.

PROM PROM stands for Programmable Read Only Memory. It is a memory chip on
which we can store a program. But once it has been used, we cannot erase its
stored information or use it to store something else. It can be programmed only
under special conditions.

EPROM EPROM stands for Erasable Programmable Read Only Memory. We can erase its
stored information by exposing it to ultraviolet light. EPROMs are cheap and

reliable and hence they are widely used.
EEPROM EEPROM stands for Electrically Erasable Programmable Read Only Memory.

The information written on it can be erased using electrical signals.

Secondary memory

Secondary memory is known as auxiliary memory or external memory . It is used to store
information for a longer period of time. It is needed because primary memory of a
computer is insufficient to store and save large amount of data for future reference and
retrieval.

Let us now discuss some of the secondary storage devices.
1. Hard disk : A hard disk is also known as a fixed disk . It is

the main secondary-storage device found inside the cabinet
of a CPU. It can store large amount of data up to 8 TB. All
the work done on a computer can be stored in a hard disk. A
hard disk is made up of many rigid metal plates coated to
store data magnetically.

6