Question about dual channel DDR2

If a motherboard has 2 memory slots that are configured to run in dual channel mode, do both RAM sticks need to be the same to take advantage of the dual channels? Could you run a 2gb and a 1gb together and have 3gb running in dual channel mode? Or would it revert to 'normal mode'?

What if the motherboard has 4 memory slots; channel A and channel B. Assuming that dual channel requires identical sticks, what would be the best way to configure 3gb of RAM in a 4 slot dual channel mobo? Would you put a 1gb and 512mb stick in channel A and in channel B; or the two 1gb sticks in channel A and the 512mb sticks in channel B; or would it matter?

Thanks.

 

Not all motherboards with 4/6 slots can take 4 memory modules.

Some are either DDR or DDR2 or even DDR3 in pairs.

 

Dual channel memory is sold in matching pairs that the manufacturer determines are identical in properties thru testing. Just buying the same thing twice will not give you true dual channel. But in my experience the difference between buying a matched pair and using two separatly bought but identical model sticks is nominal. So I go with whatever is the least expensive, and if its separate, I'll take the 2% loss in speed.

Your motherboard manual will tell you how to setup dual channel, you cannot put a 2 gig stick and 1 gig stick of the same speed and voltage together as dual channel, the sticks must be nearly identical and the same size. So you would put the two 512's together as dual channel in channel A and add the 1gig stick as regular memory in channel B. later if you add another 1 gig of the same type memory to channel B you will see a boost in both amount or ram and speed from its dual channel capabilities.

 

No make/model.... I was asking a theoritcal question, just to broaden my knowledge of dual channel technology. And (so far) everyone has been very helpful and informative.
Thanks guys!

 

One of my PC's, an Asus A8N SLI premium mobo, it has 4 memory slots
I'm running in DC mode using a total of 1 1/2 GBs across 4 slots :major

Equal amounts of memory in each channel, but you need still need matching sizes/pairs ( just think in terms of Duals, Twins, Pairs, 2, know what I mean!):major
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My configuration =
Channel A = 1 stick of 512mb & 1 stick of 256mb
Channel B = 1 stick of 512mb & 1 stick of 256mb
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Exact brands don't matter, nor does Factory matched pairs, only that they are capable of running at identical speed's, timings and voltages, you may have to manually configure the memory speeds when SPD setting's don't match...
Sometimes SPD timings are Consertive....
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