Is memory speed dependent on CPU FSB???

[Styler2K]

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.

 

[Mikki]

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

 

[Styler2K]

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?

 

[Mikki]

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....

 

[Superman9534]

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.

 

[Mikki]

Yeah, if he used a 1:1 ratio...default should be 3:4...

 

[Styler2K]

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!

 

[Mikki]

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...

 

[Styler2K]

Hey Mikki,

But with 4:5, will my RAM run at DDR333?

I'm getting the impression from other threads that I won't...

 

[Mikki]

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)

 

[JSSheridan]

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.

 

[Mikki]

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