Intel Core vs AMD K8 architecture

The main challenge for the CPU designer today is the average memory latency the CPU sees. A Pentium 4 3.6 GHz with DDR-400 runs no less than 18 times faster than the base clock of the RAM (200 MHz). Every cycle the memory is being accessed, a minimum of 18 cycles pass on the CPU. At the same time, it takes several cycles to even send a request, and it takes a few cycles to send a request back. (We discussed this in the past in our overview of memory technology article.) The result is that wait times of 200 to 300 cycles are not uncommon on the Pentium 4. The goal of CPU cache is to avoid accessing RAM, but even if the CPU only has to go to system memory 4% of the time, that 4% of the time can lower performance significantly.