Asus P5B-Plus and TWIN2X1024-6400C4 incompatible?

Hi all,

Can somebody tell me outright if Corsair TWIN2X1024-6400C4 will work as PC2-6400 800MHz in an Asus P5B-Plus?

In either single or dual channel configuration, with either one or two DIMMs present, the BIOS only appears to recognise it as PC2-4300. There is a note in the manual regarding ODT and scaling down to 4300 for incompatible memory. I first tried Geil memory, which wasn't on the QVL. So I switched to the Corsair only to find the exact same problem.

According to my P5B-Plus manual, CM2X1024-6400C4 are on the QVL and should work. According to the Corsair memory configurator, however, my mobo isn't on the list (http://www.corsairmemory.com/configurator/memory_results.aspx?id=11520).

Note the P5B-E-Plus is on the list, but that's a different board.

If anybody knows the answer to this it would be greatly appreciated!

Thanks Ramguy,

But the issue here is that my motherboard never detects the memory as what it should regardless of what the FSB is running at. I can't even run this memory at 667MHz PC2-5300. I really need to know if I have a compatibility issue with the board and why my manual and Corsair say different things.

At any rate why would I need a 1066 FSB CPU to run the memory at 800?

What happens if you are running at 70 Miles an hour but the traffic in front of you is running at 60 Miles an hour?

ABS? :):

My FSB multiplier is 4. 166x4=667 or thereabouts. My motherboard supports 800MHz DDR2. I've seen nothing anywhere to suggest that my FSB must be higher than the frequency of the memory. Surely not? Let's just shoot for 667MHz to simplify things. Yes, it is overclocking the CPU and yes, that could account for all sorts of problems.

However, my problem is the motherboard detecting PC2-4300 regardless of what the FSB is running at. Does this memory work in this board or not?

Again to clarify, my motherboard manual says this:

Some old version DDR2-800/667 may not match Intel's On-Die-Termination requirement and will automatically downgrade to run at DDR2-533. If this happens, contact your memory vendor to check the ODT value.

I need to know if I'm running into this problem with these Corsair modules. The POST detection of PC2-4300 suggests that I am. Does anybody know the true relevance of this? Should I be able to ignore what was detected and just wind the memory speed higher? Or is it a limiting factor?

I realise I may never reach DDR2-800 because I can't run my CPU on a 200MHz FSB, although there are many, many people successfully doing this on a Pentium D 805.

I realise I may be unlucky and I can't even run my CPU on a 166MHz FSB, and therefore can't reach DDR2-667.

However I'm not talking about overclocking. I'm saying that my system only ever detects this memory as PC2-4300 Dual Channel Interleaved. My manual says that incompatible RAM will be underclocked, and this is the what I'm trying to ascertain. Once I know categorically what the problem is, I can spend more money and replace parts. I'm not asking for an exchange or for help overclocking my system. I just want some facts that are very hard to come by without help from the vendor.

I'm also very curious about your suggestion that I should be using a 1066 FSB to get DDR2-800 speeds from my memory. Traditionally one would just pair the FSB to the memory's maximum rating. Is there a special reason why this is no longer so in today's DDR2 world?

I'm afraid you've only answered a different question. CPU-Z output indicates PC2-6400. Everything is correct. I've tested both modules individually with memtest. I'm sure the memory is just fine.

Default FSB speed is indeed 133MHZ and yes that's DDR2-533. However I have no problem exceeding that speed to roughly 150MHz. At all times the RAM detects as PC2-4300. It's not this speed on the SPD and it's not running at this speed, so this indicates a compatibility problem. This is documented behaviour in my motherboard manual and I must contact the memory vendor.

I've come to the conclusion that it's my motherboard. There are many obscure references to this kind of problem on the web. I don't require any further help. If I eventually fix this, I'll post my results here.

I'd still like an explanation on why my CPU must be on a 266MHz bus in order to work with 800MHz RAM. My understanding is that it works the other way around. A 200MHz bus requires 800MHz RAM and a 266MHz bus requires 1066MHz ram, at least if the FSB multiplier is 4, which mine is. By telling me this you are suggesting I change parts, which means spending money. Most people will not do this without some sort of technical explanation.

I too own a P5B-Plus, and the EXACT kind of memory modules you have. The only difference is that I have a C2D E6420... The memory runs fine! The timmings are pretty lose right now though (SPD JEDEC standard). Ill be playing around with thoses soon! Anyways, Im kind of puzzled as to why your pentium D is running @ 133Mhz FSB when it should run 200 stock (Am I missing something here?).

*The only issue Ive had with this mobo so far is CPU temps monitering. Its been comfirmed with a ASUS rep that it reads 14.7C over what your cpu really is running @ in idle. 20C or so @ 100% load...

*Edit: Gah, just looked up and found out that the 805 is a 533Mhz Quad pumped FSB, my bad... I think the CPUs FSB bandwith is the culprit.

I'd still like an explanation on why my CPU must be on a 266MHz bus in order to work with 800MHz RAM.

Actually, 800Mhz ram will work fine with a 200FSB chip (I underclocked my cpu to that just to make sure). However, anything higher than a 1:2 FSB:DRAM ratio and this mobo wont like it! So yeah, your CPU is the bottleneck. Maybe its time for you to upgrade to a better CPU. If your looking for something cheap, a Pentium Dual Core E2160 would do the trick or even a C2D E4300 if you can spare a bit more cash...