Can someone please explain ddr speeds/bandwidth to me?

[Energize]

I understand that Intel Core 2 Duo cpus are quad data rate, so their fsb data transfer rate is 4x their fsb clock speed. I also understand that the memory cells of DDR2 modules runs at 1/4 of their data transfer rate, and the i/o bus runs at 1/2 the data transfer rate because they are double data rate.

But if a cpu with a fsb data transfer rate of 1,333MT/s has 10,664GB/s of bandwith, but a single DDR 800 module will only provide 800MT/s, 6,400GB/s of bandwidth, I cannot see how it can provide enough bandwidth for the cpu unless it runs in dual channel mode?

 

[Energize]

Surely someone must know?

 

[googly]

What does it matter? If you're a hard-core gamer/benchmaker you're going to buy whatever is touted as the latest & greatest. Others just make do, knowing that it's better than their last buld

 

[Comdrpopnfresh]

Dual channel doesn't really increase bandwidth a noticeable amount. You're also taking latencies out of the equation. The latencies on memory mean that data is readily available quite quickly. The true bus speed on this theoretical system is 333mhz. The speed of the ram in this system... 400 mhz. You're also neglecting the call to the FSB, transfer across FSB to North Bridge, and then row and column addressing calls for the memory- and the differential between the read and write. Modern processors are not strapped for bandwidth, so you're assumption that memory hold back the processor is untrue. There are many other factors. Such as the tiered set of caches present in a computer which mask the latency issues of the under-tier. L1 masks L2, which masks NB mem controller latency. Disk cache hides spindle latencies. I wouldn't loose sleep over the whole thing

 

[SerpentRoyal]

Core speed is KING. Stick with quality 1.8V DDR2 1GB 800 RAMs for best compatibility and performance. Run at 1:1 memory divider and relaxed timing to discover the maximum stable core speed. Use memory divider to overclock RAMs if needed. 450-480MHz @ 4-4-4-12-2T is usually best with Intel CPUs.

Noobs spend wayyy too much $ on fancy RAMs and PSU.

 

[her34]

Originally posted by: Energize
I understand that Intel Core 2 Duo cpus are quad data rate, so their fsb data transfer rate is 4x their fsb clock speed. I also understand that the memory cells of DDR2 modules runs at 1/4 of their data transfer rate, and the i/o bus runs at 1/2 the data transfer rate because they are double data rate.

But if a cpu with a fsb data transfer rate of 1,333MT/s has 10,664GB/s of bandwith, but a single DDR 800 module will only provide 800MT/s, 6,400GB/s of bandwidth, I cannot see how it can provide enough bandwidth for the cpu unless it runs in dual channel mode?

you are assuming core2duo needs 10gb bandwidth in the first place. just because it has support for it, doesn't mean it needs all of it. does a mouse perform worse on usb1 instead of usb2?

there are benchmarks of single vs dual channel that show for most common applications (encoding, games, etc) dual channel only adds a few percentage points if that. this indicates that the 6gb from single channel is enough to keep the cpu fed and busy 100% of the time

if a widget maker can make 4 widgets a day, it doesn't matter if you drop off the materials to make 10widgets at his workplace in the morning. he can only make 4 widgets a day and supplying more material doesn't change that.

likewise if core2duo only needs 4gb bandwidth (a made up number) to stay 100% busy, then you wouldn't see a performance penalty from using single channel and only supplying 6gb bandwidth to the cpu.