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2 sticks of ram in dual and 1 stick in single?

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September 16, 2011 8:32:26 PM

Hello I have two OCZ DDR2 PC6400 800Mhz 1Gb memory sticks that came as a matched pair and four sockets on my motherboard. Now I know these can run in dual channel mode but recently I bought one 2Gb stick of exactly the same make and speed etc with slighty different timings. Can the first pair run in dual mode with the extra 2 GB individual run in single or will the whole thing run in single mode. Thanks
September 17, 2011 10:41:39 AM

I think what you mean is single and dual channel, you will still run the single channel memory but nothing in dual until you run the 4th module.

Here is a link explaining dual channel interfacing, very interesting.

http://en.wikipedia.org/wiki/Dual-channel_architecture
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September 17, 2011 11:37:49 AM

My old 3-slot nForce2 chipset can run 1GB dual-channel mode by installing 2x256MB modules in the first channel slots and a 512MB module in the second channel slot. Not sure about your chipset, though.
Maybe you should try this and see if it boots in dual-channel mode.
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a b } Memory
September 17, 2011 12:24:33 PM

Not sure about ZenithCS's claim of duel channel over 3 dimms (sticks of memory), but that would be very rare to the point where I doubt it to be true, and if it is true then it is very rare indeed. Most older systems had 3 slots as a holdover from the PC133 days, and if you wanted performance then you would use 2 in duel channel, but if you needed bulk space (at the time 768MB was considered HUGE) then you would run 3 in single.
Memory itself is single channel. There is no advanced logic on the memory sticks themselves to make them communicate with each other in order to work together. Everything is done through the north bridge (NB) (a chip that has been integrated into the processor on AMD systems for years, and is just now beginning to disappear on the Intel side). The NB is the computer that runs and manages your motherboard's fast and high priority devices (while the south bridge (SB) controls legacy and slower devices, and company specific features).
To run your system as duel channel you have to have matched pairs of memory. The timings have to be the same for all modules, and if they are not then the faster memory will be under-clocked in order to match unless you slightly overclock your ram through BIOS to compensate by manually specifying the timings (not hard to do, and most ram can be over clocked a little bit with no harm).
Some people claim to have huge performance hits if they do not buy ram kits to run their memory as multichannel, but I have never seen this to be true for myself. Perhaps it is merely a high end thing, or a DDR3 thing. But over the years I have built and worked on several DDR and DDR2 rigs and seen similar performance weather I bought a kit, or found single sticks for a very good price. I have even mixed and matched brands with no problem at all. So long as your timing and speed ratings match it should be fine. To those who think a kit is required; do you think the manufacturer is going to test each pairing for best performance? The chips come off a convayer belt, are tested for speed and timings ability, and then are put in their packaging. If all they are doing is matching timings and speed, you are perfectly capable of the same thing.
In short, you should buy a 4th stick of ram, or trade it in for 2 smaller sticks of ram (are you running a 64bit OS so you can see more than 3.5GB of memory?). But try it, you may not know the difference unless you are doing some real gaming or other performance oriented task.
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a c 104 } Memory
September 17, 2011 1:25:52 PM

What motherboard do you have?

Read the manual.
It should explain exactly what will happen with the odd stick of ram.

Some motherboards allow the matched pair to run in dual channel mode, and the odd pair will run in single channel mode.

It may be a moot point.
The loss in real application or FPS performance in single vs. dual channel mode is usually small. Detectable by a synthetic benchmark, but not by the user.

Adding more ram will normally benefit more than any minor cpu performance loss.
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September 18, 2011 12:35:25 AM

Thanks for the detailed replies. I have windows xp 32-bit but am about to upgrade to windows 7 64 bit so I can only see 3 gb of my 4 gb at the moment anyway. as in Zeniths post, I though that it would be impossible to have 3 sticks of ram all running dual channel because you would simply need two memory busses for the remaining 512mb single stick which you cant if it is one stick. hmmmm. anyway I have an asus m2n-vm dvi and cpu z says its all running in single channel. I dont even know how to find out if the pair is running in dual and the individual is running in single through cpu z as it only tells me one thing
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September 18, 2011 12:44:26 PM

Robbo please i have pasted a wiki link it explains everything and answers all your questions in more then enuogh detail it will only be runnning a single channel interface with the setup you are running also:

+1^ Cae "Not sure about ZenithCS's claim of duel channel over 3 dimms (sticks of memory), but that would be very rare to the point where I doubt it to be true, and if it is true then it is very rare indeed. Most older systems had 3 slots as a holdover from the PC133 days, and if you wanted performance then you would use 2 in duel channel, but if you needed bulk space (at the time 768MB was considered HUGE) then you would run 3 in single."

I know this to be true very, very unlikely.
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September 19, 2011 11:09:39 PM

i actually couldnt find where it said what happens with 2 matched and 1 single but i'll take your word for it. But why cant the matched pair run in dual channel mode and the single stick run in single channel?
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a c 104 } Memory
September 20, 2011 12:41:29 AM

robbo99 said:
i actually couldnt find where it said what happens with 2 matched and 1 single but i'll take your word for it. But why cant the matched pair run in dual channel mode and the single stick run in single channel?


Again, it depends on what motherboard and chipset you have.

On some, (mostly current), Intel chipsets, the evenly distributed capacity can run in dual channel mode, and the remainder in single channel mode.
The wicki link describes this. It is about 12 lines down under Operation.
I know this to be true for P67.
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September 20, 2011 10:17:47 AM

This again is true the newer chipset boards support this you are running a slightly older model being the case that the RAM is DDR2
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November 26, 2012 7:42:02 AM

I know this is a very old post and so i don't know if i would be getting any response to my question...

After reading through all this i had a question of my own..

I have Core i5-2500k
Asus P8P67m motherboard
and
Kingston 2x2 GB DDR3-RAM running in dual channel.

Now my question is,

I buy one more stick of Kingston 4GB DDR3-RAM, then can I put {2x4} together to work in dual channel and 2gb in a single channel mode??

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