Computer Memory - Types and Units

Computer memory is the storage space in computers where data and instructions to be processed are stored, either for temporarily or permanently.

The data is stored in the memory unit of CPU. The data storage is in binary digits 0 & 1

• 1 Bit = 0 or 1
• 8 Bits = 1 Byte 
• 1024 Byte = 1 Kilobyte (KB) (1 to 3 digits)
• 1024 Kilobyte = 1 Megabyte (MB) (4 to 6 digits)
• 1024 Megabyte  =  1 Gigabyte (GB) (7 to 9 digits)
• 1024 Gigabyte = 1 Terabyte (TB) (10 to 12 digits)
• 1024 Terabyte = 1 Petabyte (PB) (13 to 15 digits)
• 1024 Petabyte = 1 Exabyte (EB) (16 to 18 digits)
• 1024 Exabyte = 1 Zetabyte (ZB) (19 to 21 digits)
• 1024 Zetabyte = 1 Yottabyte (YB) (25 to 27 digits)

TYPES OF MEMORY :

A. PRIMARY MEMORY/ MAIN MEMORY

It is the internal memory of the computer and forms integral part of ALU ( Arithmetic and Logical Unit ) . It provides main working space to the computers.

RAM (Read Only Memory) 

• Temporary memory which holds data and programs during execution.
• The data and programs will be lost in case of power failure
• One can write, modify , erase and read the data and programs during execution.
• It is also known as Volatile memory.

ROM (Random Access Memory) 

• Permanent memory which contains instructions to get the computer started when it is switched on.
• One can only read the stored data but, can not write, erase or modify the data.
• The data and programs will not be not be affected in case of power failure
• It is also known as Non-Volatile memory.

3 Types of ROM:

1) PROM (Programmable Read Only Memory)

2) EPROM (Erasable Programmable Read Only Memory)

3) EEPROM (Electrically Erased Program Read Only Memory)

Cache Memory 

• It is the path between the processor and memory.
• It stores the program (or its part) currently being executed or to be executed within a short period of time.

B. SECONDARY MEMORY/ AUXILLIARY MEMORY

• External and permanent memory.
• It is also known as backup storage device.

Example :-

> Floppy Disk

> Hard Disk

> Optical Disks ( includes CD-ROM, WORM (write-once-read-many) and Erasable (can be erased and reloaded)

> Pen drives

> Memory Cards

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