Types of Memory

In a computer, all the programs are stored on a hard disk drive. Whenever you access any program, it is temporarily stored in the memory called RAM(random access memory) so that the CPU accesses this software quickly. Apart from RAM, there are different types of memory that have their own roles in computing. Let’s explore different types of memory and their functionality.

Computer Memory is of Two Types

1. Permanent memory
2. Temporary Memory

Permanent Memory

A memory that is not affected by the absence of electricity is a permanent memory and the data stored in it remains intact even if it is moved from one place to another. On a motherboard, it is present in an Integrated chip, also called ROM or BIOS. All the information about the motherboard, booting instructions, and functions are stored in BIOS at the time of manufacturing.

Permanent memory is of 4 types.

ROM (Read only memory). ROM, once manufactured cannot be changed. It is the static form of permanent memory. A commercially available movie or software on a CD-ROM is a good example of Read-Only-Memory. You cannot change the contents once the data has been written to it.

PROM (Programmable Read Only Memory). The hardware chip that can be programmed once is called PROM. Special Programmable kits are used to program the electronic chips. A common example is burning(writing data) on a CD-ROM or a DVD at home.

EPROM (Erasable Programmable Read Only Memory). This type of ROM has a small window on its top. If this window is exposed to UV light for a specific period of time, all the previous data is deleted. You can re-program it after the data has been completely removed.

EEPROM (Electrically Erasable Read Only Memory). This is the most used type of permanent memory. You can easily erase the data with a software program. BIOS on the motherboard is an example of EEPROM.

Temporary Memory

RAM (Random Access Memory) is another name for temporary memory. It is called temporary since all the data stored in RAM gets erased once the power is off. RAM is used to hold and execute the data or the instructions. Whenever we work on the computer, actually we are working on RAM and it’s only when we press the save button the data gets saved in permanent storage like a hard disk.

On a motherboard, RAM is present in PCB modules as shown in the figure below.

Types of RAM Modules:

Different types of RAM modules are shown above. You can differentiate these RAM modules by the CUTS on golden pins on the lower side of each module. Just notice that each type of RAM module has a cut or a notch on different positions along the length. RAM modules have been aligned vertically according to their date of origin and speed. Like SIMM modules were among the first type of memory to come and DDR4 RAM modules are the fastest and latest memory types. All the above types of RAM are Dynamic RAM.

RAM  is further classified into two types

1. DRAM: Dynamic RAM
2. SRAM: Static RAM

	DRAM	SRAM
Memory Cells Type	Capacitors	FET
Packing Density	High	Low
Speed	Low	High
Cost	Less	High
Function ( Used As )	Main Memory	Cache Memory

Working Diagram of Memory

Cache Memory 

Cache memory is just like another memory that stores the data. Although all the programs, documents, or other media files you access in a computer run in RAM to make the processing faster, the processor, instead of searching for data in main memory(RAM), reads the data from cache(SRAM). The SRAM which consists of FETs has high speed compared to RAM which is built on capacitors.

Shadow Ram

The ROM  functions relatively slower than RAM. So it takes a longer time to access codes from ROM than from RAM. In order to speed up the ROM processing, the codes of ROM are copied into a region of RAM and are write-protected. This way the system now can access the ROM codes from RAM at a much higher speed. The region of RAM where the ROM codes are copied is called shadow RAM.