Definition: static RAM

A fast memory technology that requires power to hold its content. Static RAM (SRAM, S-RAM) is used for high-speed registers, caches and relatively small memory banks such as a frame buffer on a graphics card. In contrast, the main memory in a computer is typically dynamic RAM (DRAM). Static RAM chips have access times in the 10 to 30-nanosecond range, while dynamic RAM is usually above 50 ns.

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Static RAM is fast because the six-transistor configuration of its pretzel-like flip-flop circuits keeps current flowing in one direction or the other (0 or 1). The 0 or 1 state can be written and read instantly without waiting for a capacitor to fill up or drain; however, the six transistors take more space than dynamic RAM cells made of one transistor and one capacitor (see dynamic RAM).

Earlier asynchronous static RAM chips performed read and write operations sequentially. Newer synchronous static RAM chips overlap reads and writes.

A Static RAM Cell

When opposite voltages are applied to the column wires, the flip-flop is oriented in one of two directions for a 0 or 1. At that point, the flip-flop (yellow center) becomes a self-perpetuating storage cell as long as a constant voltage is applied.