RAM or random access memory is the primary system memory a computer uses to open and run applications. RAM is used for temporary storage as opposed to the computer's hard drive which is used for long term storage of files and programs. Once the computer's power is turned off, the files stored in RAM are erased.
DRAM or dynamic random access memory is what most computer memory modules are made from. DRAM must be refreshed frequently, hundreds of times per second, in order to maintain the data stored in it. Even with constant power to the modules, if the refresh circuit does not continue to send signals to the transistors, the DRAM will dump its contents.
SRAM or static random access memory does not require refreshing. As long as power is maintained to the module, it will retain its contents. SRAM has faster access times than DRAM. According to Tech Target, SRAM has a typical access time of 25 nanoseconds while DRAM has an access time of 60 nanoseconds. Because it is faster than DRAM, SRAM is used in various components where exceptionally fast memory is most useful. SRAM is most often used for cache memory, the memory used on processors and hard drives to store frequently used data and instructions.
DRAM requires only one-sixth the number of transistors that SRAM requires. Therefore, DRAM is considerably less expensive than SRAM. The lower cost is the primary reason DRAM, despite its greater power requirements and its slow speed compared to SRAM, is the most commonly used type of RAM. Almost all RAM modules are DRAM modules.
SRAM requires four times the amount of space that DRAM modules of the same capacity do. Because DRAM only needs one transistor and a capacitor compared to six transistors needed by SRAM, it takes up much less room. This makes DRAM ideal for smaller, mobile computing systems. Although DRAM uses more power to refresh its circuits and is slower than SRAM, its smaller size and cheaper cost make it more desirable for use in standard computing.