Computer Memory Types

The Memory Technology can be classified as follows,

Read Only Memory (ROM) is a permanent memory where the data cannot be erased or overwritten. It can be used for Reading, multiple times

a. Programmable ROM is a type of ROM in which can be programmed once in the beginning. A special PROM Programmer is used for this purpose.

b. Erasable PROM is a Programmable ROM which can be erased also. It can be again Re-Programmed with the EPROM Programmer. The data is erased by passing Ultra-Violet rays onto the EPROM Chip. One disadvantage is that data cannot be selectively erased; the chip has to be completely erased and reprogrammed even for a minor change. This type of ROM was used in earlier BIOS.

C. Electrically Erasable PROM is PROM in which data can be selectively erased using Electric signals. Used in BIOS Firmware ICs etc.

Above figure shows Different types of RAM – From top to bottom:

DIP, SIPP, SIMM 20 PIN, SIMM 72 PIN, DIMM 168 PIN, DDR DIMM 184 PIN

Random Access Memory (RAM) is a volatile memory, which will hold the data only till the power is available.

a. Dynamic RAM – One type of RAM which is built with Transistors. The structure of each DRAM cell behaves like a Capacitor. As capacitors cannot hold the data for long, there is a need for refreshing circuit. It is a cheaper Memory Technology and occupies less space but the speed is comparatively lower. It is widely used as Main Memory in PC due to its simplicity in design and cheapness. This type of memory is generally used as System Memory, Video Memory etc.

b. Static RAM – This type of RAM is also built on Transistors. The structure of each SRAM cell behaves like a Flip-flop. Once you SET or RESET, it stays in the same state as long as the power is available. It is the fastest type of memory (as no refreshing is needed), but costliest memory technology and size is also big. Used as Casche in Processors.