Memory Part 2 (SDRAM & SRAM)

Base on previous article, there are 2 common types of non-volatile memory:-
SDRAM & SRAM.

SRAM stands for static random access memory. The internal circuit is base on flip-flop. It means it require a lot of transistor to represent a bit of memory.

SRAM advantage:-
- fast access time
- low static power, when there's no access to the memory, it wont drain much power

SRAM disadvantage:-
- expensive, because of many transistor it use, it use high silicon real-estate.

SDRAM stands for synchronous dynamic random access memory. It is most common type of non-volatile memory that you would find on most design. It is base on capacitor to represents a bit. Due to it capacitor base, it require some refreshing to keep the memory.

SDRAM advantage
- very cheap, (cost for 1 byte)
- a lot of R & D been done to improve it's speed comparable to SRAM

SDRAM disadvantge
- need complicated interface to access the memory. Normal I/O bus cannot access SDRAM directly. Usually there will be a SDRAM controller to access it and it require complex configurations.
- it require constant refreshing due to it's capacitive nature. this make the memory consume high power during static operations. The refereshing is usually been handle by the SDRAM controller.

Will SRAM become obsolete..?
If you look some of the embedded design, you sometimes could see design that have both SDRAM and SRAM. Usually for SRAM, it mention "battery backup SRAM". In application that require important data not to be lost, during power outage we to use SRAM backup by battery. This is possible due to it's low static power consumption.