Static RAM (SRAM)
Static RAM (SRAM) is a type of memory that is significantly faster than Dynamic RAM (DRAM). Unlike DRAM, SRAM does not need periodic refresh rates. SRAM is available with access time of 2ns or less, and can keep up with the processor running 500MHz or faster. This is possible because of the way SRAM is designed where a cluster of six transistors is allotted for each bit storage. Static RAM is often referred to as cache memory. Even with attributes such as less access time and no periodic refresh rates, SRAM is not used for all system memory. This is because; it has low density and is expensive. Lower density means the SRAM chips are physically larger but store less number of bits. Its high cost and physical constraints have prevented SRAM from being used as the main memory for PCs.