Will a third module negate dual channel goodness?

[a ronin]

Hi guys I was wondering if adding a third memory module negates the benefits of dual channel. I have on order the EPOX 8DRA+ with 2 sticks of Kingston HyperX PC3500, will adding a third in the last memory slot void the two sticks running in there or will the single channel run in tandem with the dualies?

Odd question, but I'm a first timer with performance modding.

Thanks

[_Durandal_]

How big is the third stick? I believe you can use all three slots for dual channel as long as the first two of the three slots equal the third DIMM (size wise). For instance, slots 1&2 each have 256MB of HyperX PC3500 and slot 3 has 512 HyperX PC3500 effectively giving you 1GB PC3500 in dual-channel.

If the memory modules don't follow this setup then the board should only be in single-channel.

[a ronin]

I have on order 2x512MB HyperX, so if I understand you correctly, I would need to add a 1GB module to retain the dual channel benefit? I read they don't make 1GB higher than PC3200 at present time, besides I can't afford 1GB stick anyhow.

[Nobody1]

I have 3 512MB (Corsair PC3500) populating the slots in an ASUS A7N8Xd, when it boots it displays text it's in dual channel mode, and have had no ill effects from running it as such, lastly I have neither a decrease nor increase in Sisoft mem bench or any benchmark for that matter.

[_Durandal_]

http://www.digit-life.com/articles2/...-1vs2channels/

The link above has more information about dual channel, but below I've snipped a tidbit pertaining to your case. I'll try and find a slightly more simplistic explanation though as I had to re-read this guy's explanation more than once:

What's needed for the dual-channel mode of the nForce/2? At least, two memory modules, with one installed exactly into the DIMM0 slot which is arranged differently than DIMM1/2 or DIMM1, with the DIMM2/3 being provided as well. In case of wrong installation the second memory controller might not operate. The modules can be different (as well as their producers), but their speed characteristics should be the same, otherwise the system will operate at the speed of the slower one (for example, DDR266 in case of one DDR266 and one DDR400 modules).

It's also possible to use three modules, 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.

[_Durandal_]

It appears I'm educating myself on this matter as well . The more I read the more I realize I don't know the full story yet. It appears dual-channel is somewhat similiar to RAID in that it only is as "large" as the smallest DIMM x 2. (Although some would say that at least with dual-channel the "left-over" memory isn't lost). <-- Minor sidenote

Here are some more links...pay special attention to the first one:

http://www.nforcershq.com/forum/view...ghlight=pulsar
http://forums.extremeoverclocking.co...c/49492-1.html

[a ronin]

The alingment has me confused abit. I think what it amounts to is you can have 2 of equal value, but the remainding module must be the sum (total) of the two module in dual channel.

i.e 2x256+512

[_Durandal_]

Originally posted by a ronin
The alingment has me confused abit. I think what it amounts to is you can have 2 of equal value, but the remainding module must be the sum (total) of the two module in dual channel.

i.e 2x256+512

Exactly right. However, if you have 2x256 + 1GB the amount of memory in dual-channel will be 2x256 + 512MB (running in 128-bit mode) and the other 512MB will be left running in 64-bit mode, or single-channel. Does that help?

[Eldest_One]

Ok if I am reading this correctly then I screwed up with my board. I have three dimms of 256MB's each. So does that mean that my first two slots are acting as 128MB dimms? With the third one as the 256MB that it is?

[Tigsman]

Originally posted by Eldest_One
Ok if I am reading this correctly then I screwed up with my board. I have three dimms of 256MB's each. So does that mean that my first two slots are acting as 128MB dimms? With the third one as the 256MB that it is?

lol... you tell us, how much ram does your OS or BIOS say you have?

In all honesty I think you can populate all dimm slots with the same size and type ram with no ill effects on dual channel mode.

[Eldest_One]

Originally posted by Tigsman
lol... you tell us, how much ram does your OS or BIOS say you have?

In all honesty I think you can populate all dimm slots with the same size and type ram with no ill effects on dual channel mode.

True it does report that I have 768MB's of memory installed! Oh well I guess I won't worry about it then!

[a ronin]

Originally posted by _Durandal_
Exactly right. However, if you have 2x256 + 1GB the amount of memory in dual-channel will be 2x256 + 512MB (running in 128-bit mode) and the other 512MB will be left running in 64-bit mode, or single-channel. Does that help?

Crystal.

And to the guy who said he had 3 256MB Dimms, you just sacrifice the ability to run all three DIMMS in dual channels. Like _Durandal_ said, 2x256 runs in 128bit mode (dual channel), while the remainding module will only operate at 64bit (single mode). I read it had to do with the memory banks which the motherboard has 8. So having 2 dimms running in DDR which fetches instructions on both the rise and fall cycle, taking up 4 from the dual channels setup and with DC running, you get 2 more banks taken up... now that only leaves 2 banks left for one DIMM to contend with. In order for this remainding DIMM to get the most out, you need to match or 'synch' with the rate in which your other two DIMMS are running at, thus having the sum of the DC will balance the load.. something like that :/

sorry for the half arsed explanation.

[_Durandal_]

Boy, we brought out the big boys w/ this post didn't we .

To Eldest_One:

Having three 256MB DIMMS, for a total of 768, doesn't mean you're getting cheated out of 256MB of memory. It simply means that 128MB of it is running in 64-bit mode (aka single-channel) while 512MB is running in dual-channel. My guess is that while this would seem to hinder performance some it's not noticeable enough to the user. Besides, isn't the increase from single-channel to dual-channel roughly 5-10%, thus the loss might be only 1-3% (note: I'm guessing here)?

[a ronin]

I don't quite understand either hence my query in here

Here is a pretty good explanation but requires a high aptitude to understand and right now the only thing on my mind is sleep

http://www.cpuplanet.com/features/ar...0231_1587771_2

[notdrugged]

So, basically, running the CPU at 400FSB or higher, and using dimms all three of the exact same size, if you remove one PC3200 dimm from the dual-slot controller leaving one in that controller and the other in the single-slot controller, there is no noticeable performance increase? What are two sticks running in single channel benchmarking at, also? Who else has actually taken the time to test this? I don't really feel convinced yet after reading everything here. The only definitive thing I see is that the single-slot controller needs to be the sum of the two modules in the dual-slot controller. Does the bios just check to see if the slots are filled or if Dual Channel is working?