Why is RAM speed-rated?
CPU chips come in a wide range of speeds. The fastest CPUs demand RAM that can keep up with them. Therefore, RAM has speed ratings. Until recently, those ratings were expressed in nanoseconds (ns), which is the shortest length of time in which a chip can respond to a request for information. Typical speed ratings were 60 or 70 ns. When the Pentium III appeared, and later the Celeron, memory speed was specified according to the speed of the memory bus, which, in computer terminology, means the traces on the motherboard that connect the memory to the CPU. A motherboards memory bus usually operates at 66 MHz, 100 MHz, or 133 MHz, with the higher numbers being faster. The 66 MHz motherboards are used on slower processors, like Celerons (but newer, faster Celerons will soon get 100 MHz buses). Pentium IIIs running at up to around 600 MHz benefit from a faster bus, running at 100 MHz. So do the Athlon chips. Finally, the latest Pentium III chips can use an even faster bus, running at 133 MHz
