# Introduction to memory and memory units

• Difficulty Level : Easy
• Last Updated : 21 Jun, 2022

Memory devices are digital system that store data either temporarily or for a long term. Digital computers to hard disk have built in memory devices that can store data of user or manufacturers. The data either be in the form of control programs or programs that boot the system. Hence, to store such huge amount of data the memory devices must have enormous capacity. The challenge is to build memory devices that have large capacity but cost effective. The memory devices must be capable of storing both permanent data and instantaneous data.

Memories are made up of registers. Each register in the memory is one storage location. The storage location is also called a memory location. Memory locations are identified using Address. The total number of bits a memory can store is its capacity

A storage element is called a Cell. Each register is made up of a storage element in which one bit of data is stored. The data in a memory are stored and retrieved by the process called writing and reading respectively.

A word is a group of bits where a memory unit stores binary information. A word with a group of 8 bits is called a byte
A memory unit consists of data lines, address selection lines, and control lines that specify the direction of transfer. The block diagram of a memory unit is shown below:

Data lines provide the information to be stored in memory. The control inputs specify the direct transfer. The k-address lines specify the word chosen.

When there are k address lines, 2k memory words can be accessed.

### Following are some important memory units :

Bit (Binary Units): bit is a logical representation of the electric state. It can be 1 or 0.

Nibble: it means the group of 4 bits.

Byte: a byte is a group of 8 bits.

Word: it is a fixed number of bits, it is different from computer to computer, but the same for each device. Compute store information in the form of words.

### Following are conversations of units:

Kilobyte (kb): 1kb = 1024 byte

Megabyte (mb): 1mb = 1024 kb

Gigabyte (gb): 1gb = 1024 mb

Terabyte (tb): 1tb = 1024 gb

Petabyte (pb): 1pb = 1024 tb

Refer for RAM and ROM, different types of RAM, cache memory, and secondary memory

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