Computer Memory

What is a Computer Memory and Their Types?

It stores or saves instructions and results, the results can be saved permanently as well as temporarily. The data or instruction once saved can be retrieve or recall or review whenever user demands.
They can store huge amount of data and information as per requirements. The user can use the data whenever needs. The Computer Hard Disk used as a memory has the capabilities for storing volumes of data such as songs, movies, pictures, software’s one can easily get access to this data whenever or wherever user demands. Users can be rest a sure of their data, as the data is stored almost permanently.

Computer Memory can be classified basically into three types:

1.            Primary Memory

2.            Secondary Memory

3.            Cache Memory

Primary Memory:

It is also called as the Main Memory or Internal Memory. It stores the data for processing and the Program instructions. It is also the Immediate Access Memory. It is temporary memory and of limited capacity. The standard base capacity for Primary memory starts from 640 KB, 1MB, 2MB, 8MB, 128MB, 256MB, 1GB, 2GB, 4GB etc. (in multiples of 2). Depending on the needs of the user. 

 

Functions of Primary Memory:

·        It holds the OS instructions while the computer is booting.

·         It temporarily holds the input instructions from the input devices while the data is being input and processed.

·         It stores the results temporarily until it is transferred to the respective output devices.

Types of Primary Memory

1.    RAM – Random Access Memory

·         Static RAM 

·         Dynamic RAM

2.    ROM – Read Only Memory

·         PROM – Programmable Read Only Memory

·         EPROM – Erasable Programmable Read Only Memory

·         EEPROM – Electronic Erasable Programmable Read Only Memory 

RAM – Random Access Memory

It is a read/write memory. Data can be stored by addressing one RAM cell. The data and programming instructions fed via the input device are stored in the RAM temporarily until that program is used. RAM may be updated.

 

There are two types of RAM

·         Static RAM – It retains the stored information until the computer is working.

·         Dynamic RAM – It retains stored information only until the program is working and loses the information once the program execution is completed.

ROM – Read Only Memory

It is a permanent memory. The instructions can only be read by the computer. The instructions related to system operations are stored here. These instructions are written by the manufacturer and cannot be edited by the user. When the system is turned ON, ROM instructions are instantly executed and used in operation of all I/O devices.

 There are three types of ROM

·         PROM – Programmable Read Only Memory

·         EPROM – Erasable Programmable Read Only Memory

·         EEPROM – Electronic Erasable Programmable Read Only Memory

·        PROM (Programmable Read Only Memory)

It is a non-volatile memory. Instructions can be written once by the programmer and then subsequently read.

·         EPROM (Erasable Programmable Read Only Memory)

It is an improvement over the PROM chips. Instructions can be rewritten by the programmer using special techniques. The instructions are erased using UV light and rewritten. To change the instructions the chip has to be removed from the machine and then put back after the changes have been made.

·         EEPROM (Electronic Erasable Programmable Read Only Memory)

It is advancement over EPROM, and the chip need not be taken out from the machine. Instead the programming is done using software. These chips are used in Point-of-sale (POS) terminals to record price related information and can be updated as and when needed. However they are expensive compared to the normal ROM chips.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than main Memory. These are used for storing data/Information permanently. Contents of secondary Memories are first transferred to main memory, and then CPU can access it. For example: disk, CD-ROM, DVD etc.

Characteristic of Secondary Memory

·         These are magnetic and optical memories

·         It is known as backup memory.

·         It is non-volatile memory.

·         It is used for storage of data in a computer.

·         Computer may run without secondary memory.

·         Slower than primary memories. 

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.