Need clarification on dual-channel DDR

[rayduh]

on MSI 875P NEO FIS2R.

I have two "matched" 512 MB PC2100 DDR sticks. If I plug them into the two adjacent DIMM slots [Dimm1 and DIMM2, both CH A]. (single-channel) I think that I will get 1 GB of memory running at the 266 MHz DDR rate [133 MHz clock] CPU runs at 1.995 GHz.

If I plug one in CH A [DIMM 1] and one in CH B [DIMM 3], (dual-channel) I think that I will run at twice the speed [533 ??] but only have half the memory [512 MB]. [clock and CPU say the same]

Nothing else would seem to make sense, HOWEVER the "diagram" on page 2-8 of the mamnual seems to say that I would have 1 GB running at 533 MHz.

Which is correct ??? If it is really 1 GB at 533 why would one ever use the first [single-channel] option ???.

A friend will be getting the mobo tomorrow. She is in VA and I am in PA attempting to help her, but I am confused on this issue. Will be using the 3.0 CPU. Using PC 2100 until more funds are available for PC 3200.

{another thing that worries me is all of the bad things that I read about this mobo in these forums, but that's another issue}

 

[KF]

You will always have 512 + 512 =1 G.

I'd guess the rationale for the other DIMM slot is to make up half of the memory using two DIMMs instead of one.

 

[Jeff7]

I have two "matched" 512 MB PC2100 DDR sticks. If I plug them into the two adjacent DIMM slots [Dimm1 and DIMM2, both CH A]. (single-channel) I think that I will get 1 GB of memory running at the 266 MHz DDR rate [133 MHz clock] CPU runs at 1.995 GHz.

If I plug one in CH A [DIMM 1] and one in CH B [DIMM 3], (dual-channel) I think that I will run at twice the speed [533 ??] but only have half the memory [512 MB]. [clock and CPU say the same]

Just so you know, they will run at the 133MHz clock speed regardless of being in single channel or dual channel. It's just that, with dual channel, there's two separate channels through which to talk to the system memory. It's not like dual channel is twice as fast as single channel either; it gives a performance boost, but nothing major, at least that's been my experience with my 8RDA+ motherboards.

 

[mechBgon]

On the i875P, the dual-channel memory feature is approximately analogous to RAID0 with two hard drives, if that helps. The controller welds them into one 128-bit-wide (or 144-bit-wide) memory channel, which is why the modules need to be of identical organization (eg, can't use one double-sided and one single-sided module for dual-channel).

With nForce2, there are two memory controllers that load-balance between two 64-bit channels that remain independent, which is why it can do DC with three modules and non-identical ones.

 

[rayduh]

Thanx to all responders. I genuinely appreciate the answers, all correct BTW. I now that in dual mode I will have 1 GB. Also confirmed by a respose from Intel.

 

[rayduh]

Thanx to all responders. I genuinely appreciate the answers, all correct BTW. I now that in dual mode I will have 1 GB. Also confirmed by a respose from Intel.

 

[rayduh]

Thanx to all responders. I genuinely appreciate the answers, all correct BTW. I now that in dual mode I will have 1 GB. Also confirmed by a respose from Intel.

 

[rayduh]

Sorry for the multiple posts. I'm having connection problems. Also, I do not know how to delete the extra posts.

 

[JetBlack69]

Originally posted by: rayduh
Sorry for the multiple posts. I'm having connection problems. Also, I do not know how to delete the extra posts.

Don't worry about them.

 

[RalfHutter]

Originally posted by: rayduh
Sorry for the multiple posts. I'm having connection problems. Also, I do not know how to delete the extra posts.

Just consider that you're posting in "Dual-Channel"!

 

[Jeff7]

Originally posted by: mechBgon
On the i875P, the dual-channel memory feature is approximately analogous to RAID0 with two hard drives, if that helps. The controller welds them into one 128-bit-wide (or 144-bit-wide) memory channel, which is why the modules need to be of identical organization (eg, can't use one double-sided and one single-sided module for dual-channel).

With nForce2, there are two memory controllers that load-balance between two 64-bit channels that remain independent, which is why it can do DC with three modules and non-identical ones.

Though they may not have to be the same size - I've got a 512MB stick working in DC mode with a 256MB stick on my secondary system; thing is, both are Geil RAM, from the same product line, bought from Newegg. I can't guarantee that this'll always work though. Both sticks are double sided.

Edit: And next time, I'll read BOTH paragraphs before posting....

 

[gramboh]

Just to clarify, you have an 865/875 based mainboard and have 1 x 512 in one channel and 1 x 256 in another channel and dual channel is enabled? Did you use Sandra to see if the memory bandwidth did infact increase? I didn't know it was possible to do this.