Will a third module negate dual channel goodness?

[Senor Panadero]

Does the bios just check to see if the slots are filled or if Dual Channel is working?

I think it is both simpler and more complex because there are different issues.

The "Dual Channel" thing happens if both memory controllers have memory, period. Whether it is the same size module, number of chips or whatever, it is in dual channel mode for at least a certain amount of memory and there will be a small performance increase because of that, and yes, folks have demonstrated it. The demonstrations are not impressive because the performance increase for dual channel is small, and the benchmarking we are talking about is with something like Sandra, which is about the best we can do for accuracy. The figure I usually see in the forums works out to about 2-10% increase in a bandwidth test, with two equal modules closer to the 10%, and closer to the 2% for 3 dimms of the same size.

At the same time, adding more modules, such as 3 vrs 2 and more memory chips obviously has an impact on how high a FSB you can reach, and sometimes how low you can set the timings just as it always has. This is really noticeable and is the subject of many complaint threads when that magic 200FSB all of a sudden turns into a 190, or even a 185 when a large third module is added, or if two 512's are exchanged for two 256's. There are usually 2 or 3 threads active on this subject alone in Asus at any particular time.

So balancing the memory betwen controllers is not necessary for dual channel performance increases, however, as the quote from _Durandal_ says, it seems optimal if it is.
JMO
YMMV


Ever so cool that there is a memory forum, I can move nearly all threads now.

[notdrugged]

Thanks, bro

[crazyhorse_aba]

I was just getting ready to post a thread about this. I am going to use 3 sticks myself and need some imput on how to populate dimms on nf7-s board to stay in dc.
2- corsair 256mb 32x64 pc-3200llpt
1- corsair 512mb 64x64 pc-3200llpt

[_Durandal_]

You need to put those memory sticks in the following way:

2x256MB sticks in slots 1&2
1x512MB stick in slot 3

There are three links within this thread, one of which is from the nforcehq forums. If you get a chance it would definitely help to read it . *Hint* it's the sixth post down .

[Senor Panadero]

Here is a pic.

[a ronin]

Thanks for the picture, I've always had some suspicion as to which one was which. Now to add to my original question. I bought some OCZ 2x256 PC3200 EL series memory to run in dual channel, but I cannot afford another 512MB just yet so I was hoping to use the old stick of 512 PC2100 in the remainding slot.

Question is then, if I put in 512MB of PC2100 I will bump my memory down to that speed, but will the extra 512MB gains outweigh having higher frequency or not? Hope my line of questioning is understandable.

[Senor Panadero]

Ugh, that is a bit ugly.
You could try booting with the 512 only, then manually set the FSB, memory frequency, and memory timings to best comply with the 512. Then install all the rest and see how a boot with a Memtest goes.
IMO, this would outweigh any gains, unless you really need that memory for specific applications.

[smilepak]

Actually it will work with all 3 being of the same memory. I currently have it running now in my system.

Slot 1: 512MB PC2700
Slot 2: 512MB PC2700
Slot 3: 512MB PC2700

When bootup, it reconzie as dual channel and work nicely.