Random Access Memory (RAM)
RAM stands for ‘Random Access Memory’ and is often called the memory or main memory of computer. It is made up of semiconductor chips, hence also called primary memory. It is the working space used by the computer to hold the program that is currently running along with the necessary data and instructions. It is fast and expensive memory which allows the computer to access the data and instruction very quickly. It is mainly used to store the following:
- Kernel of running operating system.
- Data and instruction currently being processed.
- Data and instruction waiting to be processed.
- Information waiting to its output.
- Currently arrived data and instruction from input system.
It is called RAM because its contents can be accessed randomly. We can read from RAM as well as write into it. Hence, it is also called ‘read-write’ memory. The main drawback of RAM is that it is volatile memory so the contents of RAM are lost when the computer is switched off.
It is made of millions of microscopic cells which are distinctly numbered so that each cell can be identified and located. The memory cells are also called memory locations. Each cell be be electrically charged or not. The charged cell represents 1 and not charged cell represents 0 in binary format.
Types of RAM
DRAM stands for ‘Dynamic Random Access Memory’. It is the most common and cheapest type of memory chip. It is made of capacitors which is capable of storing the electric charge. Due to leakage of charges, the capacitors discharge gradually and the memory cells lose their contents. DRAM has to be refreshed periodically by recharging
the capacitors to retain its memory contents. It is slower than SRAM but it is dense, consume less electricity, smaller in size and less expensive.
Synchronous Dynamic Random Access Memory (SDRAM) is DRAM that has a synchronous interface which is widely used in present computers. Traditionally, DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs. SDRAM has a synchronous interface, meaning that it waits for a clock signal before responding to control inputs and is therefore synchronized with the computers system bus. From the original SDRAM, further generations of DDR (Dual Data Rate), DDR2 and DDR3 have developed, and DDR4 is currently being designed and anticipated to be available very soon.
SRAM stands for ‘Static Random Access Memory‘ and it is made of transistors. It is called static because it can remember or retain its memory contents without being refreshed or recharged as long as there is power. SRAM does not need to be refreshed or recharged periodically like DRAM. SRAM is faster than DRAM but more expensive, loser in density and bigger in size and consumes more electricity.
Differences between SRAM and DRAM
The compare and contrast between SRAM and DRAM can be shown by the following table:
|1.||DRAM stands for Dynamic Random-Access Memory||1.||SRAM stands for Static Random Access Memory|
|2.||DRAM is made up of capacitors||2.||SRAM is made up of transistors.|
|3.||DRAM is high density RAM. (In one chip larger memory can be constructed.)||3.||SRAM is low density RAM. (In one chip small amount of memory can be constructed.)|
|4.||. Power consumption of DRAM is higher than SRAM.||4.||Power consumption of SRAM is lesser than DRAM.|
|5.||DRAM need to be periodically refreshed. (System automatically refreshes the RAM cells.)||5.||SRAM need not be periodically refreshed.|
|6.||The cost of DRAM is lower than SRAM||6.||The cost of SRAM is higher than DRAM.|
|7.||The data access time is larger than SRAM, typically requires larger than 40 nanoseconds. Hence, they are slow.||7.||The data access time is smaller than DRAM, typically less than 30 Nanoseconds, Hence they are fast.|
|8.||DRAM is generally used for low cost high capacity memory for computers.||8.||SRAM is generally used to create memory of critical section like cache memory.|
|9.||For example: DDR, DDR2, DDR3 (Dual Data Rate), EDO DRAM, SDRAM, RIMM etc.||9.||For example, cache memory of microprocessor.|
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