The capacity of an individual memory chip is often given in terms of bits. When discussing the capacity of an entire memory system, however, the preferred unit is a byte , which is commonly accepted to be 8 bits of information. Note the convention that lower case b is the abbreviation for bit and upper case B is the symbol for bytes. The performance of a memory system is defined by two different measures, the access time and the cycle time . Access time, also known as response time or latency , refers to how quickly the memory can respond to a read or write request.
Several factors contribute to the access time of a memory system.
The main factor is the physical organization of the memory chips used in the system. Other factors are harder to measure. The bottom line is that the response time for a memory system is usually much longer than the access time of the individual chips. Memory cycle time refers to the minimum period between two successive requests. A simple, if old, example of a memory with a long cycle time relative to its access time is the magnetic core used in early mainframe computers.