Static RAM and Dynamic RAM

Computers use both static and dynamic RAM. Here we will find out what are the differences of these two categories of RAM considering following aspects:

How these two types are designed
How these operate
Issues with each type
What is the most fast and what is most cheap
Where these memories are used in our computers

Dynamic RAM
This is the most common type of RAM in use today. In a dynamic RAM chip, a bit is stored in a single memory cell. Each memory cell includes a transistor and a capacitor these transistors and capacitors are extremely small so that a single chip can hold millions of memory cells.

How these cells operate
In a memory cell, the capacitor holds electrons to store a 1; to store a 0, the capacitor is emptied. The transistor serves as a switch to allow the memory controller of the chip to read or change the state of a capacitor.

Problem with dynamic RAM
The problem with capacitors is capacitors have leakages so those can’t keep electrons for a long time without getting discharged frequently. So in a dynamic RAM either the CPU or the memory controller has to recharge all capacitors which stores 1 before those get discharged. This automatic refresh has to take place thousands of times per second. This refresh process takes time and slows down memory operations.

Static RAM
Static RAM stores a bit in a completely different mechanism called flip-flop which does not need a recharge.

Ok now what’s wrong with Static RAM?
To implement a flip-flop it takes 4 or 6 transistors so when compared to dynamic RAM Static RAM take more space so that makes less memory per chip and it takes much more parts to store a bit. Due to these two reasons, Static RAM has become very expensive.

Where in our computer these two memories are used?
Since Static RAM is fast and expensive whereas Dynamic RAM is cheap and slow, the speed sensitive cache area in the CPU is created of Static RAM while the large RAM area is made of comparatively cheaper Dynamic RAM.

Further reading (Flip-Flops): http://en.wikipedia.org/wiki/Flip-flop_(electronics)
Source: http://computer.howstuffworks.com/question452.htm