Static RAM and Dynamic RAM

One of the very important parts of the computer is the memory, and is as important as our memory. Any thing we do or we see, stored in our memory and we can retrieve it again, which is the same as the computer memory, however, the main difference between the computer’s memory and ours is that we have one type of memory and the computer has many.

Two of these types of the computer’s memory are the static RAM, (or SRAM) and the dynamic RAM, (or DRAM). In this presentation we will compare the SRAM and the DRAM, and talk briefly about their construction and their use in the computer.

Dynamic Random Access memory (DRAM)
DRAM is made up from transistors, which store the state of binary digit as a charge built up on transistor called, a Field Affect Transistor (FET). This method is the most popular, because of its ease of manufacture and hence its cost effectiveness. However it is more complex to operate than static RAM, because the stored charge leaks away very quickly and gets lost, if it is not tipped up as frequent intervals, which means that extra electronics, have to be put into the system to carry these operations. The consequence of this topping up cycle is that the speed of access for dynamic RAM is slower than the speed of the static RAM.

Static Random Access Memory (SRAM)
It is more expensive to produce. As more transistors are needed for the storage of each byte. However, static RAM, does not have to be topped up. As data is stored by monitoring the state of a transistor, being used as switch, rather than a charge storing mechanism as is the case with dynamic RAM. The technology inside the static RAM chip, is a little different instead of being stored as a leaky charge, the transistors, are permanently switched into an ‘on’ or an ‘off’ state, and this do not need constant attention, in terms of topping them up.

Comparing between the SRAM and the DRAM

Static RAM (SRAM)

1. 4 times more expensive
2. Very low access time
3. Can store ¼ as much
4. Information stored on RS flip-flops
5. No need for refreshing

Dynamic RAM (DRAM)

1. Low cost
2. Consumes less power
3. Can store 4 times as much
4. Information stored on FET transistors
5. Needs to be refreshed

To sum up briefly, we say that Both the SRAM and DRAM are volatile. This means that if the power of the system is off, then all the data stored in them would be lost. However because the SRAM is a fast memory it is used in a (cache memory) which comes between the CPU and the dynamic RAM, in this way the data can be processed quickly, by the processor, which mean that the processor, will get the immediate data from faster static RAM.
As on the other hand, because of its low cost and its high capacity, which is four times as much as SRAM, the DRAM is used for main memory.

References

1. Clements, Alan. The Principles of Computer Hardware, 3rd ed. (Oxford University Press, 2001).
2. Stallings, William. Computer organization and architecture: designing for performance, 5th ed. (New Jersey, Prentice Hall, 2000).