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Question about Dual Channel Memory

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Question about Dual Channel Memory

Old 01-28-04, 04:16 PM
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Question about Dual Channel Memory

I searched but came up empty.

I have an nForce2 mobo that has 3 memory slots, two of which can be used for dual channel mode. My question is what effect does adding another stick to the third slot have? Say I have identical 256MB PC3200 sticks in dual mode, and I want to add a 512MB stick or just another 256MB stick. What effect should I expect? Do the identical sticks still perform in dual channel mode?
Old 01-28-04, 05:28 PM
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an odd design, but I see it's point. Here is a decription that is better than me typing it out in my own words


but remember that the dual-channel access can be set only for the memory size equal to the double size of the first module (which is installed into the slot of the lowest number), and if the size of the first module does not exceed the sum of the sizes of the second and third modules. Obviously, there are two most optimal cases: equal memory modules inserted into the first and second slots, or three modules, with the first one being equal to the sum of the other two modules.
Make sense?
Old 01-28-04, 07:43 PM
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Well, I do see what the quote is saying, but it does not make sense in light of how I thought dual channel mode works.

Here's how my mobo works for dual channel: Use slot 1 or 2 for the first stick and slot 3 for the second stick. If I understand that quote right, then I could put an equal speed stick of 512MB in slot 1 and the two sticks of 256MB in slots 2 and 3. Then I would get the benefit of dual channel and more memory, right?

BTW, where did you get the quote? I'd like to see what else there is to say about this. Thanks!

Last edited by RalphWiggum; 01-28-04 at 07:49 PM.
Old 01-29-04, 11:27 AM
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Yes, you understand the quote right.

A "channel" of ram is really a bank, not just a single DIMM.

it is possible for a 'bank' of ram to be one dimm socket or two or even four.

Dual Channel desgins have 2 independent memory controllers.

Dimm slot 1 is accessed by one memory controller
Dimm slots 2 and 3 are accessed by the other

Dimm slot 1 is one bank
Dimm slots 2 and 3 are one bank

If you have 512mb in bank one
you MUST have 512mb in bank two in order for dual channel to work

in the case of this chipset, the 512 in bank two can be one 512mb dimm in slot 2 or two 256mb dimms in slots 2 and 3. It considers both the same.

I can see value in this, but it is an odd design.

Search google for Dual Channel and your motherboard model number, you will find a ton of info. It seems many people can not get their nfroce2 boards into dual channel mode no matter what they try.
Old 01-29-04, 12:48 PM
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so how do you know if you are in dual channel mode ?
Old 01-29-04, 12:55 PM
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Originally posted by timewaster
so how do you know if you are in dual channel mode ?
To know for sure, run a benchmark and compare your results with benchmark built in matrix or compare to your own machine with only one DIMM installed.

I imagine your motherboard documentation or support web page would have more info on how to enable. Not all boards are the same.
Old 01-29-04, 02:48 PM
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In regards to your 3 DIMM nForce2 mobo, DIMM 1 & 2 are in a pair, and DIMM 3 is further away. Your original configuration w/ the two 256MB is placed in DIMM 1 and DIMM 3. The way nForce2 dual channel works is DIMM 1 + DIMM 2 = DIMM 3. So if you want to add more memory, you'll simply move the two 256MB to DIMM 1 and 2, and buy one 512MB and put it in DIMM 3. My nForce2 mobo's DIMM sockets are color coded (DIMM 1&2: Purple, DIMM 3: Green), so there can be no confusion on where to the RAM.

Originally posted by timewaster
so how do you know if you are in dual channel mode ?
When you boot up the system, the post will tell you Dual Channel DDR400, or whatever memory you're running. If you're slow just download CPU-Z and click on the Memory tab.

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