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Random Access Memory

The random-access memory (RAM) supports both read and write operations. Integrated circuit RAM comes in two main types:

static RAM in which a single bit of memory is simply a digital flip-flop and requires only continuous power to maintain its state.
dynamic RAM in which a bit of memory is a storage capacitor in either the charged or discharged condition. The term dynamic refers to the need to periodically renew or refresh the slowly discharging capacitor.

Compared to dynamic memory, static memory has the following advantages. It is simpler to use, about ten times faster and more reliable. On the other hand, it is more expensive, consumes more power and requires more physical space. Because of power consumption in an IC the largest static RAM is 16K bits. The largest dynamic RAM is 260K and hence is used for normal applications while the static RAM is used for special fast applications within the same computer. Both types of RAM are volatile, meaning that stored information is lost when power is removed from the chip. Some computer designs provide a limited amount of non-volatile read/write RAM storage by using special low-power (and slower) dynamic memories powered by re-chargeable batteries.

Doug Gingrich
Tue Jul 13 16:55:15 EDT 1999