Computer Storage Definitions and Notations

Computer EngineeringComputer ScienceOperating System

Computer storage contains many components that are used to store computer data. Some information about the various storage devices is given below.

Computer Storage Definitions

The computer storage devices include Primary and Secondary Storage devices. These are explained in detail as follows −

Primary Storage Devices

Primary storage is also known as the main memory and is the memory directly accessible by the CPU. Some primary storage devices are −


ROM is read only memory. This memory cannot be changed, it can only be read as required. Since ROM is unchangeable memory, it is used by data and programs that are frequently required and seldom changed, like the system boot program.


RAM is random access memory. It is volatile i.e. the data in RAM is lost when the power is switched off. RAM is the major form of primary memory as it is quite fast. However, it is also quite expensive.

Cache Memory

Cache is used to store data and instructions that are frequently required by the CPU so it doesn't have to search them in the main memory. This is a small memory that is also very fast.

Secondary Storage Devices

Secondary or external storage is not directly accessible by the CPU. The data from secondary storage needs to be brought into the primary storage before the CPU can use it. Secondary storage contains a large amount of data permanently.

The different types of secondary storage devices are:

Hard Disk

Hard disks are the most famously used secondary storage devices. They are round, flat pieces of metal covered with magnetic oxide. They are available in many sizes ranging from 1 to 14 inch diameter.

Floppy Disk

They are flexible plastic discs which can bend, coated with magnetic oxide and are covered with a plastic cover to provide protection. Floppy disks are also known as floppies and diskettes.

Memory Card

This has similar functionality to a flash drive but is in a card shape. It can easily plug into a port and removed after its work is done. A memory card is available in various sizes such as 8GB, 16GB, 64GB, etc.

Flash Drive

This is also known as a pen drive. It helps in easy transportation of data from one system to another. A pen drive is quite compact and comes with various features and designs.


This is short for compact disk - read only memory. A CD is a shiny metal disk of silver colour. It is already pre-recorded and the data on it cannot be altered. It usually has a storage capacity of 700 MB.

Computer Storage Notations

There are several storage notations. These are given in detail as follows:


A bit is the smallest unit of memory storage. It can contain either 0 or 1. The value of a bit is usually displayed by a low and high in electrical discharge for 0 and 1 respectively.


The nibble contains 4 bits. It can also be represented as half a byte.

1 Nibble = 4 Bits

Byte (B)

A byte is formed of 8 bits. It is used to store the value of characters, special symbols etc.

1 Byte = 8 Bits

Kilobyte (KB)

A kilobyte is approximately 1000 bytes or 1024 bytes to be more precise.(2 to the 10th power)

1 KB = 1024 Bytes

Megabyte (MB)

A Megabyte is 1024 Kilobytes or 10,48,576 Bytes.

1 MB = 1024 KB

Gigabyte (GB)

A Gigabyte is roughly a billion bytes or 1024 MB.

1 GB = 1024 MB

Terabyte (TB)

A Terabyte is 1024 Gigabytes.

1 TB = 1024 GB
Published on 09-Aug-2018 17:40:56