Random Access Memory – Meaning And Types Of RAM

Random Access Memory And Types Of Ram – A Ram constitutes the internal memory of the CPU for storing data, program and program results. It is read/write memory. It is called random access memory (RAM) since access time in RAM is independent of the address to the word that is, each storage location inside the memory is as easy to reach as other location & takes the same amount of time.

We can reach into the memory at random & extremely fast but can also be quite expensive. RAM is volatile, i.e. data stored in it is lost when w switch off the computer or if there is a power failure. Hence a back up uninterruptible power system (UPS) is often used with computers.

RAM is small, both in terms of its physical size and in the amount of data it can hold. RAM comes in the form of “discrete” (meaning separate) microchips and also in the form of modules that plug into holes in the computer’s motherboard. These holes connect through a bus or set of electrical paths to the processor.

Types Of Ram

(i) Static RAM (SRAM) – The word ‘static’ indicates that the memory retains its contents as long as power remains applied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors.

Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis. Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher. Static RAM is used as cache memory as cache memory needs to be very fast and small.

(ii) Dynamic RAM (DRAM) – DRAM, unlike SRAM, must be continually ‘refreshed’ in order for it to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second.

DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells. These cells are composed of one capacitor and one transistor.

A Dynamic RAM stores information in the form of charge on a capacitor, which leaks, away in a very short time. Therefore its contents must be periodically refreshed after every two milli-seconds. A memory cell of DRAM stores only on bit either O or 1. The DRAM consumes less power and is cheaper then the SRAM. DRAM covers less, space on computer’s motherboard. It is produced in large sizes. A DRANM needs only one transistor per memory cell and hence its package density is High.

Difference Between Static And Dynamic Ram

SRAM retains its contents as long as electrical power is applied to the chip. Hence it has long data lifetime.DRAM has an extremely short data lifetime, typically about for milli seconds.
There is no need to refresh.Need to refresh continuously.
FasterSlower as compared to SRAM
Used as cache memoryUsed as RAM
Larger sizeSize is Less
ExpensiveLess Expensive
High power consumptionLess power consumption

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