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- May 6, 2003
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What are they, my motherboards have had it I just never used it as I usually just have one stick. Will it help/hurt an o/c with a good sticks, or what? TIA.
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InThrees said:My understanding is that dual channel does little to nothing at sync'd speeds.
emericanchaos said:basically with these types of chipsets FSB isn't the bottleneck it's the other side of the memory.
"where's the bottleneck?" [/B]
Andy71600 said:I have been told that the advantage is minimal on amd cpu's, but on intel's that is a different story
EDIT: yay 3 stars
InThrees said:Dual channel effectively removes any A-sync penalties you would otherwise incur by running your memory at a lower speed.
Before dual channel, if memory capped at a speed lower than the processor and motherboard, overclockers would run the lower FSB sync'd with the highest memory speed possible.
Because of how dual channel works, if your memory capped at something like 170mhz but your mobo and processor could do 218 mhz, you could set the memory ration to 80% and enjoy all the bandwidth you would have at a 170mhz sync'd rating, but have more overclocking options due to the capability (headroom) of your mobo / proc.
Basically, it really ONLY helps if your memory can't even come close to doing what your processor and motherboard can do.
And in the end, because of how FSB / multipliers interact, it only lets you get maybe 100 more mhz out of your processor, because it gives you more options in overclocking.
In the above example, here are two ways you could run your system:
10 x 218 @ 4/5 = 2180mhz cpu, 170mhz memory / 218mhz fsb
12.5 x 170 @ 1/1 = 2125mhz cpu, 170mhz memory/fsb
The above assumes that your proc and board can do 218 fsb stable, and the processor absolutely is not stable beyond 2180mhz.
Also, in the above example, system performance is basically identicle, with very small differences here and there.
My understanding is that dual channel does little to nothing at sync'd speeds.
timmyqwest said:
Good read, i've never really looked at it that way...maybe i should try some tests with this
Gautam said:
My friend tried running 200mhz fsb 6/5 in dual channel for a 183mhz memory bus speed, or theoretically a 732mhz effective data rate. You would think that the bandwidth would not be limited by the memory bus, but it in fact was very much so- only 2400 MB/sec; not the 3200 that one would expect. Dual channel seemed to have done nothing.
hitechjb1 said:Single Channel vs Dual Channel DDR Memory Module
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Summary:
Dual channel or single channel mode in nforce2 mb is not that crucial for overall performance. The difference is only few % (say 2-3%) at most. Also single channel may let FSB to go a bit higher due to a smaller chance of potential dual dimm mismatch and memory controller stress at high FSB, I think. On the other hand, dual channel memory controller provides some performance advantage due to its intrinsic speculative caching capability. At this point, the little higher FSB from single channel offset the performance advantage of dual channel, and the two is about a tie, I think, for AMD mb. For some nforce2 mb that have integrated video which can benefit from twice the nforce2 memory bandwidth, since the bus between the video and the memory controller has 2x64 bit bus.
The max bandwdith between memory controller and CPU would be 2 x 8 x FSB = 16 FSB MB/s. x2 is because of DDR (data are transferred at both rising and falling edge of the FSB clock, x8 because of 8-byte bus or 64-bit bus). The effective bandwidth, taking into memory controller (~95% efficiency), would be around 15.2 FSB. E.g. FSB = 200 MHz, effective bandwidth ~ 3040 MB/s.
Dual channel makes a big difference for P4 dual channel mb though, due to quad pump data of P4 (or QDR). The max bandwidth for P4 dual channel is 4 x 8 x FSB = 32 FSB MB/s. The effective bandwidth, taking into memory controller overhead (~ 75% efficiency), would be around 24 FSB MB/s.
For single channel, max bandwidth = 16 FSB, effective bandwidth ~ 15.2 FSB. Hence the improvement of effective bandwidth of dual channel = (24 - 15.2)/15.2 = 58% for P4 dual channel system over single channel.
E.g. FSB = 200 MHz, effective bandwidth ~ 4800 MB/s, which is around 60% more than that of a nforce2 mb running same FSB 200 MHz.
E.g. running fsb:memory=5:4, with FSB=250, memory=200, effective bandwidth ~ 24 x 225 = 5400 MB/s.
hitechjb1 said:Dual Channel, Nforce2, P4 and AMD FSB
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3. IMHO, running slower memory in ASYNC at 50-66-75% is much more price/performace effective than 100% SYNC. 50% memory cost will get to 10-15% of the max bandwidth. This approach has been used in P4 dual channel since its FSB is QDR (quad pump data) and there is no fast memory to match at that speed, and dual channel is the only way to fill up the system bandwidth.
For AMD DDR system, ppl who want absolute performance will just use the fastest memory to match the FSB and run them in SYNC to get the last 10% of memory bandwidth.
In summary, for AMD nforece2, the effective bandwidth running in SYNC mode = 0.95 x 2 x 8 x FSB = 15.2 FSB MB/s. E.g. FSB = 200 MHz, effective bandwidth = 3040 MB/s. FSB=225 MHz, effective bandwidth = 3420 MB/s.
For P4 dual channel, the effective bandwidth running fsb:memory=1:1 (SYNC mode)= 0.75 x 4 x 8 FSB = 24 FSB MB/s. E.g. FSB = 200 MHz, effective bandwidth = 4800 MB/s.
E.g running fsb:memory=5:4, with FSB=250, memory=200, effective bandwidth ~ 24 x 225 = 5400 MB/s.