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Read Only Memory (ROM)

Information stored in ROM is permanent in nature, that is, it
holds the data even if the system is switched off. It holds the

starting instructions that are required to start a computer. It
is also called non-volatile memory.

Secondary Memory

This memory is permanent in nature and The human brain can hold about 2.5

is not directly accessed by the CPU. It petabytes of information, equivalent
allows users to store data that may be to a TV show being played for
approximately 342 years non stop.
easily retrieved. It is cheaper compared
to primary memory.

Secondary memory devices are also called
secondary storage devices. They are categorised into three types:

Secondary Storage Devices

Magnetic Disk Optical Disc Flash Drive

Hard Disk Solid State CD DVD Blu-ray Disc Pen Drive Memory Card
Drive (SSD)

Magnetic Disk

A circular metallic disk covered with a magnetic coating, that is used for storing

data, is called a Magnetic disk. You can record and erase data on a magnetic disk any
number of times.

Hard Disk

The hard disk consists of one or more magnetic disks called
platters. Each disk in the hard disk has top and bottom

surfaces on which data is recorded using a magnetic head. It
is permanently fixed in the computer system. It is usually used
for permanent mass storage. The most important function of
the hard disk is to store program files and data files.

The hard disk comes in a variety of sizes with storage capacities as high as 12 TB
(Terabyte) or even more. The CPU accesses data stored on a hard disk much faster

than it can access data on a CD.

Data Storage and Memory 9