What is Memory in computer world learn full Details in Desi language.

Memory:- Memory is the storage area of the computer to place instructions and data it called memory. It is categorized into primary (main memory) and the secondary memory(Permanent memory).

Memory Hierarchy:- The computer requires different kinds of memory for its proper functioning. Since the fast memories are very expensive, they cannot be used in excess. There is hierarchy of memories considering their speed and cost. The registers are the fastest storage devices; even faster than the cache memory (SRAM), which is faster than the main memory. The primary or memory the secondary memory. The hierarchy of various types of memory is shown in Figure:-

(Figure hierarchy).

The memory can be two categories according two the hierarchy:

1. Primary Memory:- The primary memory is also called as the main memory and is of two kinds:

A. Read Only Memory (ROM) 

B .Random Access Memory (RAM).

A. Read Only Memory (ROM) :- In read only memory (ROM), data is recorded on an integrated circuit by the manufacturer. Once the data has been recorded, it cannot be changed. The content of ROM can be read but it cannot be modified; hence the name is read only memory. It is designed to perform a specific function that is not changed, and generally instructions are required for initialising the devices stored in ROM. For example, ROM is used in most computers to hold the basic input and output system (BIOS) so that the computer's hardware such as hard disk, RAM, I/O ports and peripherals are recognised when the computer is switched on; and then the operating system is loaded.

The ROM is categorised into various types such as.

A.PROM,

B.EPROM

C.EEPROM

 B. Random Access Memory:-This is the primary memory from where data and instructions can be retrieved in a random manner using a unique memory address. Hence, the name is random access memory (RAM). It is a volatile memory in which the contents are lost once the power is turned off. This kind of memory is used to store the data temporarily during the computer operations.

The RAM is mainly of two types: static RAM and dynamic RAM.

2. Secondary memory:- The secondary memory are the storage devices in which the data can be stored for longer duration, and it is not lost even when the power is turned off. This memory has greater storage capacity than the primary memory. Also, it is inexpensive, but slow.

There are two types of access to stored data in secondary storage devices:

A. Sequential Access:- The stores device used for sequential access is magnetic tape.

B. Direct Access:- The various stored device used for direct access are grouped. 

3. Cache Memory :- the cache memory is a SRAM placed between the CPU and the main memory and when CPU needs any data or instruction for processing , it first searches the cache memory If the required data or instruction is found in the cache memory it is retrieved by the CPU for processing otherwise, the main memory is searched for the same information .

It is three classified as:

(I) Instruction cache:- The cache only hold instructions.

(II) Data cache :- The cache only holds data.

(III) Unified cache :- The Cache holds both instructions and data.

There are different levels:-L1, L2 and L3.

If all the three levels of cache are present in the system, then data is fetched in the order: L1>L2>L3>RAM. This means if data is not present in L1,L2, would be checked followed by L3 and then RAM

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