ddr2 memory

[inuyashafly]

I am now starting to consider build ing a new computer. so I started window sopping for memroy. ddr2 seems to have like 2 times the cas latency can someone tell me whats up?

 

[Mondoman]

When measured in *clock cycles*, you're right. However, what humans care about is actual time; to figure that out, you've got to figure out how long a single clock cycle lasts for the different RAMs. DDR2-800 runs at 400MHz, so a clock cycle is 1/400,000,000 second. DDR-400 runs at 200MHz, so a clock cycle for it is 1/200,000,000 second. Thus, clock cycles for DDR-400 are twice as long as clock cycles for DDR2-800, so a CL2 DDR-400 memory has the same CL delay time as a CL4 DDR2-800 memory.