Dual Channel Memory Dilemma

[potissimus]

Hi there. Right now my computer consists of a 1Ghz Athlon CPU w/ KT266A chipset and 256MB of DDR266. I am looking to upgrade to an Athlon XP 2500+ w/ an Nforce2 chipset for better gaming and to a lesser extent regular applications.
As we all know, the Nforce2 chipset has Dual Channel Memory capabilities. Because of this I have three options:

1) Order 2 sticks of 256MB DDR400 memory (probably Geil) and use it along with my DDR266 memory for a total of 768, but with different speeds, and not using the Dual Channel Technology.
2) Order 2 sticks of 256MB DDR400 memory (probably Geil) and get rid of or sell my stick that I have now. This way my overall memory MBs would be lower (512 instead of 768), but I'd be using the Dual Channel technology (and i think the mem runs at higher speeds if its just DDR400 w/o the DDR266...this right?)
3) Order 1 stick of 512MB DDR400 (probably Geil) and use my DDR266 stick I have now, therefore using dual channel technology but using two different brands and types of memory.

So...which solution would get me the best performance?
Thanks in advance.

 

[Excelsior]

AFAIK, as long as you have 2 of the same sticks in the first 2 slots, youll have DC even if you have a 3rd stick. Even then...Id just sell the one stick of PC2100 you have now, and buy 2 256MB DDR400 sticks.

 

[Lord Evermore]

If your board has 3 memory slots, all 3 can be operating in dual-channel mode. However not all of the memory can be accessed in DC mode. The nforce2 is not a symmetrical memory channel design.

For most boards, slots 1 and 2 are linked to the first channel, and slot 3 is the second channel. If you put two modules of 256 in each of those, and one module of 512 in slot 3, then you end up with each channel having a total of 512MB, all of which will operate in dual-channel mode. If you have a 256MB module in slot 3, then all of that module, and 256MB of memory from the first channel (not necessarily all in one module) will be accessible in dual-channel mode, and the remaining 256 in the first channel will be used in single channel mode. Performance that way of course isn't as good as full dual channel, but it's better than all single channel.

The nforce2 doesn't care whether the modules are exactly the same type, like Intel chipsets do. As long as the amount of memory on each channel is the same, all of it will run in dual-channel mode.

The speed is not as important. If you have a 333MHz bus Athlon, then running the memory at 333MHz (PC2700) is the best because synchronous operation results in the lowest latencies. Running the memory at a higher speed than the frontside bus isn't really needed in an Athlon system, especially a dual-channel system, because one channel of memory at the same speed as the FSB can supply all the bandwidth needed; with two channels, there's already double the needed bandwidth.

If you have a 266MHz bus Athlon, then memory at 266MHz is the best performance match.

Naturally, if you buy a 333MHz bus Athlon, or heavily overclock a 266MHz bus processor, then PC2100 memory will slow you down because it may not handle the higher bus speeds. Running the memory slower than the processor will result in a performance hit due to latency penalties, even though the bandwidth would still be enough.

Your best solution will depend on the type of processor you're going to use, and whether you'll be overclocking. Assuming a Barton 2500+, you will need to get rid of your current memory because it won't run at 333MHz. So you'll need to order 2 modules in order to run in dual-channel mode. You can order PC2700 or PC3200, depending on the prices and how much you want to spend, and considering whether you might want to overclock or reuse the memory later with a 400MHz bus processor.

 

[potissimus]

Alright. Thanks! It seems that I had not researched dual channel technology as much as I should have. Wasn't aware that you could have all 3 slots in use and still use it. So I guess in my case I'll be selling my PC2100 memory since the 2500+ has a 333Mhz FSB. Thanks for the tip!

 

[Lord Evermore]

It only applies to the nforce2. Intel's P4 chipsets require multiples of two and they have to be the same size and organization, otherwise it goes to single-channel mode. RDRAM chipsets require multiples of 2 at all times (except if your board uses "32-bit" modules which is just two modules integrated into one).

 

[potissimus]

Oh, alright. Thanks for the info.

But now this brings up another question:
What memory will get me the best performance? I've read numerous reviews and have pretty much narrowed it down to three choices. All of these are dual channel "optimized" memory and I can get each of these for about the same price ($130-$140).

-Corsair 2x256MB PC2700 TwinX (Dual Channel)
-Geil 2x256MB PC3500 Dual Channel
-OCZ 2x256MB PC2700 Dual Channel

I will probably do some light overclocking, but nothing too much. I've heard mixed opinions on the reviews and can't find this exact situation on the boards. Recommendations?

 

[Lord Evermore]

Corsair is the most popular of the three, because they have a long history of good memory and have always been a high-performance maker. Geil I think is relatively new, don't know much about them. OCZ had some troubles and got a terrible reputation for good reason, but is now under new management entirely and some people feel they are doing good now.

The only thing that TwinX or other dual-channel kits have over other memory, is that the maker put two modules into a motherboard and ran memory tests on them together. If they ran without errors (I don't know really what sort of "testing" they run), they packed them up together. If they didn't, then one or both of the modules may have been bad so they probably retest them to find out which one. There's no optimization of any kind, other than that they've tested them and they guarantee dual-channel operation with each other will work.

Many of the prices I've seen for Corsair, it's actually cheaper in the TwinX kit than individually.

Naturally of course, if you're not overclocking, the PC2700 is all you need.

 

[potissimus]

Yeah, the only reason I am opting for the dual channel memory is price, as you stated.

I was also thinking that I don't need more than than PC2700. In the many reviews that I read, it seemed that the Corsair and OCZ PC2700 were good sticks, while the Geil PC2700 was not as good. However, I also read that the Geil 3500 is a great stick and, while it is a higher DDR bandwith, it only costs as much as the OCZ and Corsair sticks. Thats why I'm curious as to Geil especially in terms of performance compared to the other two...

P.S.- Thanks for the quick replies!

 

[potissimus]

Well, I think that I've decided. Corsair is the highest priced and after resulting to reading even MORE reviews/benchmarks, doesn't offer that much more performance than OCZ or Geil.

With Corsair out, I'm down to Geil and OCZ. At PC2700, the Geil can't compete with the OCZ, but the PC3500 can at similar pricing. However, I just found that the OCZ came with a $10 discount with the new FIC AU13 Nforce2 motherboard. This kinda tipped me, so I'll be getting the OCZ EL Dual Channel PC2700 memory.

Thanks for your help! I now know MUCH more about memory than I did when I posted this question.