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All gates introduce a small but measurable time delay, and since flip-flops
are made of gates, it takes a small but finite amount of time to change
their value. The same is true of the tiny capacitors used in DRAM chips,
where the delay is around 70 nanoseconds. The operation of the memory must
be coordinated with the rest of the computer so the control signals (MA, WR
and MBRLD) have to be asserted at the proper times.
In order to smoothly interconnect the memory and the rest of the computer, memory operations take place during what are called memory cycles. A memory cycle is the amount of time from the beginning of a memory operation, whether a read or a write, until the end of that operation and the beginning of the next. |