Static Random Access Memory (SRAM) is a type of RAM used in various electronic applications including toys, automobiles, digital devices and computers. It only holds its contents while power is applied. This type of memory differs from dynamic RAM (DRAM) in that DRAM must use refresh cycles to keep its contents alive. SRAM holds data as a static ‘image’ as indicated by the name, until written over or lost from powering down.
SRAM is more expensive, faster, and more power-efficient than DRAM for most uses. However, its internal structure also makes it less dense, and therefore a less ideal candidate for the main memory inside personal computers. Instead, SRAM is used for critical, secondary uses, such as fast cache memory for central processing units (CPUs). CPU cache can significantly boost a computer’s overall performance with a rather small footprint of dedicated memory.
Compared to DRAM, SRAM is more power-efficient when idle. However, overclocking the CPU can negate this power-saving advantage. Overclocking causes the CPU to work faster than its marketed specifications. In such a case, the SRAM cache spends less time in the power-saving idle mode.
SRAM is also present in many modern hard drives as disk cache. The disk cache is used to temporarily store data that is accessed frequently. Retrieving data from the cache is many times faster than retrieving it from a standard, platter-designed hard drive. People might also find SRAM in modem routers, printers, digital cameras, and compact disk (CD) or digital versatile disc (DVD) decks. Toys with electronic interfaces also commonly use this type of memory.
Static RAM can be synchronous, or asynchronous. Asynchronous SRAM is not dependent on the clock frequency of the CPU, while synchronous synchronizes with the CPU clock speed.
SRAM can be incorporated into one of two types of transistor chips: the bipolar junction transistor, or the metal-oxide-semiconductor field-effect transistor (MOFSET). The former makes SRAM extremely fast but also consumes a lot of power. This type of transistor is used in specialty applications. MOFSET is the more common type of memory used in the various applications discussed here.