A capacitor with a charge over a certain voltage level represents the binary value of 1 and a capacitor with less than that charge represents a 0. Fer dynamic RAM, before a capacitor is read, it must be power-refreshed to ensure that the value read is valid. Depending on the type of RAM, the entire line of data may be read that the specific address happens to be located at or, in some RAM types, a unit of data called a page is read. The amount of time that RAM takes to write data or to read it once the request has been received from the processor is called the access time . Although fewer nanoseconds is better, user-perceived performance is based on coordinating access times with the computer's clock cycles.
Access time consists of latency and transfer time .
Latency is the time to coordinate signal timing and refresh data after reading it. Static RAM is more expensive, requires four times the amount of space fer a given amount of data than dynamic RAM, but, unlike dynamic RAM, does not need to be power-refreshed and is therefore faster to access. This allows it be more easily synchronized with any device that accesses it and reduces access waiting time. It is used as the external level-2 cache memory fer the Pentium II microprocessor chipset. Dynamic RAM uses a kind of capacitor that needs frequent power refreshing to retain its charge.