Hi,
I've got an ASUS P5N32-SLI Pro with 2 gig of Corsair XMS2 6400, 4 sticks of 512. If I run the FSB at 800 I can get the machine to boot with 1:1 divider yet CPU-Z reports 1:1 at 200Mhz which looks like PC400.
If I up the FSB beyond 800 I have to use a divider to get the machine to boot. Currently I have the FSB at 944 and have to use a 7:6 divider to keep the memory as close to 800 in the BIOS, currenty (809). CPU-Z reports the memory as running at 202Mhz, which again makes it look like PC400 and not PC800.
Can someone please explain what is going on? I've read countless forums and everyone seems to have a different explanation. Ranging from CPU-Z not able to report the memory speeds correctly to running 4 sticks causes the memory handler to treat PC800 as PC400.
I've not tried running two sticks to see if I can bump the memory higher and will try that.
I do have the memory running at 2.1v and have left the timings on SPD for now.
Please someone help me figure this out.
Best regards,
Corsair XMS2 6400. What's stopping me from running at 1:1?
Corsair XMS2 6400. What's stopping me from running at 1:1?
Last edited by Westend on Fri May 26, 2006 12:58 am, edited 1 time in total.
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Apoptosis
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Well you wont be able to run a memory divider of 1:1 on an Intel DDR2 based motherboard as it's impossible to do so for a memory speed of 800MHz. To run at 800MHz memory in 1:1 you'd have to overclock your front side bus beyond what is possible.
Two popular front side bus speeds are 200MHz and 266MHz, so let's take a look at those...
FSB1066:
4:3 DDR2-400
1:1 DDR2-533
4:5 DDR2-667
2:3 DDR2-800
FSB800:
1:1 DDR2-400
3:4 DDR2-533
3:5 DDR2-667
1:2 DDR2-800
I know what you are thinking... Your front side bus is running at 800MHz, therefore your memory when running 1:1 should be at 800MHz. That is not the case. Remember the Front Side Bus on Intel platforms is Quad pumped meaning they take the FSB of 200MHz and after some work it's bumped up to 800MHz. This is why 1066MHz systems run at a FSB of 266MHz and so on.
So if you have a bus speed of 944Mhz you are really at:
944MHz bus speed / 4 (quad pumped) = 236MHz FSB
As you can see running 1:1 with your processor at 236MHz you should be seeing 472MHz on the memory.
Hopes this helps.
Two popular front side bus speeds are 200MHz and 266MHz, so let's take a look at those...
FSB1066:
4:3 DDR2-400
1:1 DDR2-533
4:5 DDR2-667
2:3 DDR2-800
FSB800:
1:1 DDR2-400
3:4 DDR2-533
3:5 DDR2-667
1:2 DDR2-800
I know what you are thinking... Your front side bus is running at 800MHz, therefore your memory when running 1:1 should be at 800MHz. That is not the case. Remember the Front Side Bus on Intel platforms is Quad pumped meaning they take the FSB of 200MHz and after some work it's bumped up to 800MHz. This is why 1066MHz systems run at a FSB of 266MHz and so on.
So if you have a bus speed of 944Mhz you are really at:
944MHz bus speed / 4 (quad pumped) = 236MHz FSB
As you can see running 1:1 with your processor at 236MHz you should be seeing 472MHz on the memory.
Hopes this helps.