C2D & DDR2 Frequencies - Advice?

[Methanoid]

OK I admit I am confused.

My C2D 6400 has run at 3.2ghz happily before (but my cooler wasnt attached properly or came unstuck) with my OCZ PC6400 memory in a Gigabyte DS3. Now it doesn't (prob due to cooling) but I also have the newer G33M-DS2R board as well.

I'm looking to buy a 2nd C2D system and wondering if I buy some cheapo PC8500 (1066) memory (ignoring issue of slower timings for now) that will be better for overclocking as I can get it set to run at a speed below its tolerance. CPU is prob gonna be a 6420.

Where I do get confused is how the mem frequencies correspond.

If I run 6400 at 3.2ghz (400FSB) using the OCZ 6400 memory can I set the memory as though it was 533mhz memory and overclock it back to its 800mhz design frequency? Pretty sure the new mobo won't allow that!

Similarly if I run the 6420 at 3.2ghz using the Cheapo 8500 memory can I set that as though it was 667mhz memory and overclock it to below its PC8500 (1066mhz) limit?

Does that make any sense to anyone? I got confused as heck when I see "memory dividers of 2.5"... aren't they multipliers?

Someone here must have worked this all out in English!!

 

[ArchAnGeL]

you just set the memory to run 1:1 (I am not familiar with the ds3 bios options) i.e in sync and it will run at double your fsb.

i.e if your fsb is 400, at 1:1 your memory will be at 800 hz

So if you get pc8500 memory which is rated at 1066 hz, you can run your fsb to 533 hz before you start to overclock your memory. This would equate to to a theoretical cpu overclock of 4.26 using the 8x multiplier (good luck!)

If when you find your cpu max overclock, the fsb is making your ram run slower than it is rated. You have a few option to benchmark and see what is quickest for you.

e.g

say your max cpu overclock is 3.6 achieved by a 450 fsb and 8 mulitplier. Your memory will be running at 900 hz

1. You can leave it a 1:1 at your stock timings (prob cas 5) @ 900hz
2. you can see if it will work at tighter timings e.g cas 4 @ 900hz
3. You can drop the cpu multiplier and go for a higher fsb e.g. 514 x 7 = 3.6 (ish) and at 1:1 your memory will be running at 1028 hz
4. You can use a higher memory divider at 450 fsb.

the question of memory multipliers and dividers is addressed here

 

[ArchAnGeL]

I am assuming that you set the memory divider in the ds3 by the actual memory speed e.g 533, 800, 1066

By setting each of these speeds you are telling the bios what to multiply the fsb by to give the memory speed.

e.g. for 533, multiply the memory speed by 1. So 266 x 2 (for ddr2 - double data rate) x 1 = 533. This is 1:1

for 800, multiply the memory speed by 1.5. so 266 x 2 x 1.5 = 800. This is 2:3

So if you have clocked you fsb to 450 and you are running 800 (2:3) your memory will be running at 450 x 2 x 1.5 = 1350 hz

I hope this makes sense. Maybe someone with better knowledge of the specific bios options on those boards can explain it better