Dual Channel Memory - What is it?

  Jester2K II 09:42 21 Aug 2003

Can anyone offer an idiots explanation for what "Dual Channel Memory" means?

If i understand correctly it something to do with putting two sticks of memory in two banks rather than one stick in one bank (ie 2 x 256 Mb instead of 1 x 512 Mb) to improve "Memory Bandwidth" ??

Does my putting 2 x 256 Mb SD-RAM in my PC count or do you need a certain type of memory to do this ?

All explanations so far assume you know more than i do...

  Bodi 10:03 21 Aug 2003

but when I set up this computer with 2 x 512MB DDR Memory modules, it came up with 133Mhz singe channel. Slot 3 seemed to hold the key, and providing this was populated - with either 1 or 2 I got 133 double channel.

Now whether this helps at all, I wouldn't know, but I thought the "S" in SDR was for single and the "D" in DDR was for double. Might be wrong tho.


  mark500 10:04 21 Aug 2003

click here This is the closest I could find to explain it. I'd never heard of it either.

  Bodi 10:12 21 Aug 2003

click here=

'Cos my understanding and explanation was as clear as mud.


  rickf 10:19 21 Aug 2003

You need to have the same modules in channel say 1 &3 or all 4. You also need to use ddr. This all depends on your mobo's ability to support it. I have two 512ddr in slots 1&3 and it seems tom increase by about 25%. That's all I know. Hope it goes someway towards clarification. If you go to the m/b's website it'll explain it.

  Rowey 10:37 21 Aug 2003

Dual channel memory ...

You need two identical memory boards and a dual channel motherboard. I don't think there are any sdram dual channel boards but i could be wrong.

A dual channel setup is supposed to increase the memory bandwidth, but as rick said it would only be between 10 and 25%.

  temp003 12:35 21 Aug 2003

Jester 2k II: Fancy you asking a question :o))

I tried some time ago to find out how exactly it worked, but couldn't find any decent articles.

My very basic and limited understanding, from what I could gather here and there, is that at the theoretical level, the chipset (or the memory controller in the north bridge) has two channels of communication (or two channels of data transfer) with the memory, instead of the previous one channel, so that the theoretical bandwidth or data transfer rate is doubled, even though the amount of memory is the same.

I think the Rambus uses a form of dual channel, well before it's introduced to DDR.

So whether you can make use of dual channel memory depends on whether the chipset used by your motherboard has this capability. Currently, as far as I know, and excluding the Rambus platform, the only chipsets (for normal desktop computers, not servers) that support it are Intel's 865 and 875 series chpipsets, and nVidia's nForce2 for the AMD platform (can't remember whether the nForce1 had it). I don't think VIA or SiS has any chipsets that support dual channel yet, but not sure. All these supporting chipsets use DDR memory only. So no go for single data rate SDRAM.

At the practical level, you must use identical modules of DDR in the sense that they have the same capacity and same speed (e.g. both are DDR400, 256MB). Theoretically I don't think they need to be the same brand, but you're just tempting fate if you don't buy the same model from the same brand.

Some memory manufacturers sell these "twin" kits. They are just 2 identical modules, but they have been tested to work together on a dual channel setup.

  Chegs ® 12:46 21 Aug 2003

Toms Hardware had a review of dual channel mobo's(I think it was their site)and elsewhere were articles on OC'ing with Dual Channel RAM.Also found a supplier of Twin DDR modules for dual channel mobo's,but nowhere could I find an "idiots guide" to what/where/how it works. :-)

  Beb? 13:06 21 Aug 2003

the S in SDR stands for Synchronous (i think thats how you spell it)

  The Sack 14:44 21 Aug 2003

Dual channel has nothing to do with the RAM, people only buy identical sticks to ensure it works. Dual channel simply refers to each channel the RAM sits in on the mobo having its own memory controler, if you look on nForce 2 mobos 1 out of the 3 RAM slots is set slightly to one side on its own so you know which one has its own controller if you are only using 2 sticks.

It is just good numbers and nothing else, an Athlon on a 400MHz FSB has a maximum bandwidth of 3.2GBs, providing you have your RAM in sync and on both memory controllers they are feeding it 6.4GBs of bandwidth. So the processor cant use it anyway. It is much more usefull for P4 systems on higher FSB speeds i would image.

  rickf 15:06 21 Aug 2003

The modules do not have to be the same brand as long as they are the same speed, capacity and type. I use 1 512ddr Samsung and 1 512ddr Winbond and they function fine. I agree though that to be on the safe side try buying the same brands.

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