Computer – Memory Units

Computer data storage, often called storage or memory, is a technology consisting of computer components and recording media used to retain digital data. It is a core function and fundamental component of computers.

Memory is primarily of three types −

  • Primary Memory/Main Memory
  • Secondary Memory
  • Cache Memory

The following table explains the main memory storage units −

S.No. Unit & Description
1 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.

2 Nibble

A group of 4 bits is called nibble.

3 Byte

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

4 Word

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

S.No. Unit & Description
1 Kilobyte (KB)

1 KB = 1024 Bytes

2 Megabyte (MB)

1 MB = 1024 KB

3 GigaByte (GB)

1 GB = 1024 MB

4 TeraByte (TB)

1 TB = 1024 GB

5 PetaByte (PB)

1 PB = 1024 TB

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 device. 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.

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.

Cache Memory

Cache memory is a very high speed semiconductor memory which 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.

Advantages

The advantages of cache memory are as follows −

  • Cache memory is faster than main memory.
  • It consumes less access time as compared to main memory.
  • It stores the program that can be executed within a short period of time.
  • It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

  • Cache memory has limited capacity.
  • It is very expensive.



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