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Is memory speed dependent on CPU FSB???

S

Styler2K

Member

Hey all,

If someone in the know can clarify this for me, that'd be great...

I'm looking at picking up an 845PE motherboard (namely, either the GA-8PE667 Ultra 2, or the AOpen AX4PE Max). However, Intel's and GA's website says that if you have a CPU with an FSB of 400MHz, even if you use a stick of PC2700, your RAM will still only run at 266 MHz.

Is this true???

And if so, can you OC a 400MHz CPU ---> 533MHz so that the RAM will run at 333MHz? I'm really unfamiliar with overclocking, thus any help would be much appreciated.

 
Yeah, you'd have to oc to get ddr333 (PC2700), unless you had a 533mhz chip, which would default to the proper speed. 🙂
 

So it is possible then?

How would you do it? What setting would you have to change?

More specifically, what setting(s) would I have to change to increase the FSB from 400 to 533MHz?
 
Depends on the mobo, but generally there'll be a setting for "CPU external freq" or something like that which you'd set to 133. And make sure the CPU/Memory ratio is set to 3:4 or whatever (depending on the board). You can probably download the manual for your board before you get it, and have a looksy. I'm sure someone here has one of those boards....🙂
 
well isn't it only 533mhz FSB if you use RDRAM? Even then its not REALLY 533mhz, its 133mhz quad pumped. But its a narrower memory pipeline then DDR-SDRAM, so even then DDR in some (or most) cases is as fast. However, it seems like if you had a 400mhz fsb P4...and used DDR you would only run at 200mhz DDR, not 266.
 

Hmmm...

It's all beginning to make sense now... Both the Gigabyte and the AOpen have only the 1:1 and 4:5 CPU/mem ratio option... That's why the Asus P4PE has a leg up on the two Mobo's... It apparently *does* have the 3:4 CPU/mem ratio...

*crap*

That's the only thing (IMO) that the Asus board has over the GA board. Feature-wise the GA wins hands down... And it's cheaper to boot!
 
Styler2K, 4:5 can be a very good thing if your cpu will oc well, but your memory doesn't. With the 4:5 ratio, your cpu is less likely to get "dragged down" by your memory than it would with the 3:4 ratio...🙂
 
Here's a little table that Thugsrook made up...🙂

5:6 = 166fsb 200mem (400ddr)
4:5 = 133fsb 166mem (333ddr)
3:4 = 100fsb 133mem (266ddr)
4:6 = 133fsb 200mem (400ddr)
3:5 = 100fsb 166mem (333ddr)
3:6 = 100fsb 200mem (400ddr)

...or you could run:
3:4 = 120fsb 166mem (333ddr)
 
Someone please correct me if I'm wrong, but I believe this is how these settings work. What the 4:5 setting will do is set the memory frequency to 5/4, or 1.25, times the CPU external frequency (aka Front Side Bus) of 133 = 166MHz. The 3:4 setting will set the memory frequency to 1.33 times the CPU external frequency of 133 = 178 MHz. HTH. Peace.
 
or
fsb:memory bus X 2 = ddr speed or
4:5 ratio, 133fsb would be:
fsb / 4 * 5 * 2 = ddr
133fsb / 4 (33) * 5 (166) * 2 (333) = ddr333
🙂
 
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