This is due to a couple of factors. First, by eliminating support for parity memory, which is more expensive than standard memory, manufacturers can lower the price of their computers. In fact, all computer systems specify a memory component speed. Ensuring memory compatibility requires conforming to this specification. A memory module's access time indicates the amount of time it takes the module to deliver on a data request.
Smaller numbers indicate faster access times.
Typical speed were 80ns, 70ns, and 60ns. Speed markings on the memory chips themselves are typically still in nanoseconds. This can be confusing, but instead measure the number of nanoseconds between clock cycles. Typically, one packet of information can travel at 100 megabytes per second. Data travels on a 100MHz, 64-bit bus at 800 megabytes per second.