Help: 533 Mhz 2.4 Ghz cpu and PC800 RDRAM?

[jeff_bdn]

I currently have two Kingston KVR800X18/256 memory modules that I wanted to use and have ordered an Intel D850EMV2 Motherboard and a P4 2.4 GHZ 533 CPU. I fear that I may have made a costly mistake.

On the kingston site I see a statement that:
"533MHz system bus requires PC800-40 or 1066MHz RIMMs"

Is there any way my KVR800X18/256 modules will work with the Intel D850EMV2 Motherboard? Will I need a 400 mhz CPU rather than a 533 mhz CPU to make this work?

I was under the impression that with a 533 CPU, the CPU to chipset bus would run at 533 and the chipset to memory bus could still be set to run at 400 thus allowing standard PC800 RDRAM like my KVR800X18/256 modules to function - is this incorrect?

Thanks very much for any advice. And sorry for my lack of RDRAM understanding

 

[Crashman]

It should work fine, because the board will detect it and back off the timings. I think the reason it's not recommended might be performance related?

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[jeff_bdn]

OK - thanks for the ressurance that I didn't make a big mistake (again). I've never had a problem with RAM compatibility before but I seem to have zero luck with RDRAM. The reason these modules are spares is that I ordered them for my other computer and they turned out to be incompatible because they were KVR800X18/256 and the ones I needed for compatibility were KVR800X18-16/256.

So when I saw the note on the Kingston site that I needed PC800-40 for a "533MHz system bus" I panicked.

I'm still not clear when you would use PC800-40 (what in the heck is PC800-40 and how is it different than either PC 1066MHz or standard PC800?

Thanks again.

 

[Crashman]

I think the command rate is higher for PC800-40.

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[jeff_bdn]

I just found the other thread about the difference between PC800 45 ns and PC800-40 40 ns.

But I just looked through the FAQ on the intel MB site (why didn't I read those before!!) and I see this which troubles me still:

"PC800 RDRAM* memory is offered with two different specifications, PC800-40 and PC800-45, both of which run at the same frequency and have identical bandwidth, but have a subtle difference in internal timing. The Intel® 850E chipset supports the PC800-40 memory when running at 533 MHz system bus. The Intel 850E chipset supports both the PC800-40 and the PC800-45 memory while running at 400 MHz system bus."

I thought that I read somewhere that the board would work with
CPU -> 533 -> Chipset -> 400 -> Memory but now I'm not so sure.

Is it all or nothing - all at 533 or all at 400?

Will "backing off" to use the PC800 45 ns memory mean that my 2.4 ghz is running at a much slower clock speed than 2.4 ghz.

I think I can still cancel my order since I've recieved no note about it yet and my card has still not been charged if I should switch from a 2.4 ghz 533 mhz cpu to a 2.4 ghz 400 mhz cpu.

I just don't know if I should stick with the 2.4 533 and hope it works or switch to a 2.4 400...

Any more advice would be appreciated.

 

[Crashman]

Sounds like a plan.

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[jeff_bdn]

So you think I should cancel the 533 and change to a 400 2.4?

 

[Crashman]

Well, if you do that....

You'd loose a lot of performance with the slower bus speed. My recommendation would be to get a non-Intel board so you get better controll over your memory timing. At the slowest settings the old PC800 should work at 3x bus speed with the 133MHz (QDR533) bus CPU.

Or another plan, get a non-Intel board and the 2.4/400 and overclock to get some bus speed back. A 2.4 at 125MHz bus (QDR500) would work fine with the slower memory at the slower multiplier (the memory would be slightly underclocked for stability) and give you 3GHz. The best board in this situation would probably be the old Abit TH7-II, as long as you plan to use that memory for the life of the board.

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