Take reading as an example. When the CPU sends an instruction to the memory, it will ask the memory to fetch the data at a specific address. After the memory responds to the CPU, it will send the data required by the CPU to the CPU. Until the CPU receives the data, it becomes a reading process. The speed is expressed by the reciprocal of the access time. For example, the actual frequency of the memory with an access time of 6ns is 1/6ns=166MHz.
