Sync Vs Async

[CCW]

It seems to be common knowledge that running memory in sync with the FSB produces the best perfromacne and ive tried it and agree but wondered if anyone knows why?

Craig

[Major]

I know a simple explanation as to why, when running in Asyn. the fsb is held up by a buffer until the memory catches up, or vise versa. The farther you get away from being 1:1, 3:2 for example the more wait states in the buffer thus a bigger hit in performance.

Thats what I understand.

[CCW]

Cheers for that, few questions.....wouldnt the RAM be held up because its the faster one of the two? Instead of the FSB being held up?

Thanks,
Craig

[Major]

IMO it goes both ways, fsb waiting for the ram in some cases and vise versa in others. Even with 1:1 there are wait states, there are simply more when you run Asyc

[CCW]

OK, thank you very much! Any one else have any more info?

Thanks,
Craig

[saaya]

you get the best results when the bandwidth from nb to cpu is the same as from the nb to the memory, otherwise youll have a btlleneck effect. so in theory running in async could be faster than sync when the bus width of either of those 2 is wider than the other. for example if the cpu to nb bus is 128bit and the memory bus is 64bit wide, running the memory at 200% of the fsb should give the best results.

i think it also has to do a lot with latencies, commands have to wait in the nb before they can be processed to the cpu or memory if one of the buses is slower/has a lower bandwidth.

[Alexandrus]

Async means async, not that one of the two(CPU or RAM) waits for the other, that would still be sync.
Async means that both run at a different clock, but since the CPU doesn't always read/process data from RAM, it's not always necessary to run both sync. It's better to run sync because it will mean less wait cycles for the CPU, but the efficiency will never by 100%.