Memory latency question

[Duwelon]

Quick latency question: is 2-2-2-5 @ 400mhz the same as 4-4-4-10 @ 800mhz

If RAM1 runs at 400mhz and latencies at 2-2-2-5
and RAM2 runs at 800mhz with latencies at 4-4-4-10

What i'm asking is: Does the latency indiciate the number of cycles, and thus each cycle goes by faster at higher speeds?

 

[TC91]

yes i think so

 

[Duwelon]

I was hoping for a more definitive answer.

 

[ss284]

Yes. Ram timings are measured in clock cycles. In the end, they are supposed to be equivalent since it takes 4 cycles at 800mhz takes the same amount of time as 2 cycles at 400mhz. There are other factors that affect this, but technically they are equivalent.

 

[BassBomb]

Originally posted by: ss284
Yes. Ram timings are measured in clock cycles. In the end, they are supposed to be equivalent since it takes 4 cycles at 800mhz takes the same amount of time as 2 cycles at 400mhz. There are other factors that affect this, but technically they are equivalent.

So we really have not gained any speed increase from DDR -> DDR2?

 

[EarthwormJim]

Originally posted by: BassBomb

Originally posted by: ss284
Yes. Ram timings are measured in clock cycles. In the end, they are supposed to be equivalent since it takes 4 cycles at 800mhz takes the same amount of time as 2 cycles at 400mhz. There are other factors that affect this, but technically they are equivalent.

So we really have not gained any speed increase from DDR -> DDR2?

Yes we have, same latency, but double the bandwidth.

 

[unr3al]

The latency is the time in milliseconds that the RAM takes to respond to a request from the CPU. So you have slightly higher latencies on RAM #2 but you have twice the bandwidth. The difference is staggering in programs that are affected by memory bandwidth, ask someone who has used CL3 DDR400 and then switched to CL5 DDR2-800.

Of course, because of the integrated memory controller, latencies are pretty much irrelevant with AMD CPUs. Unless we're talking insane latencies like 8-8-8-20 of course. But you won't pick up a tangible difference between CL4 and CL5, for example.