Computer Memory Units

Computer Memory is mainly categorized into three types they are:

  • Main Memory
  • Secondary Memory
  • Cache Memory

Computer Memory Units

The following table explains the computer memory storage units −

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.


A group of 4 bits is called a nibble.


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


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

Unit & Description
Kilobyte (KB)

1 KB = 1024 Bytes

Megabyte (MB)

1 MB = 1024 KB

Gigabyte (GB)

1 GB = 1024 MB

TeraByte (TB)

1 TB = 1024 GB

PetaByte (PB)

1 PB = 1024 TB

What is Primary 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 devices. 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.

What is 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.

What is Cache Memory?

Cache memory is a very high-speed semiconductor memory that 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.

Computer memory units