I'm confused about FSB speeds on P35 boards

[millz]

I'm looking at the Asus P5K-E/WIFI-AP board, but I'm confused by a statement on the spec page. Asus's spec page says:

While in DDR2 1066 mode, ASUS´s exclusive technology offers a choice of FSB 1333

So which is it, 1066 or 1333? Can the RAM run at 1066 (533 double pumped, I assume) when the FSB runs at 1333? Maybe I'm not understanding the relationship between the actual clock speed and the DDR RAM effective speed.

When RAM says it's DDR2 667, that means it'll run at 1333, right? Then what about RAM that says DDR2 800? Will that run at 1600? Is that faster than any board can handle?

Could someone explain this to me?

Thanks,
millz

 

[JCGhz]

Your rated fsb will default to 1333 and your ram bus speed will be 333 unless you up the rated bus speed to 400(for DDR2 800) which will up your rated fsb to 1600... you shouldnt have any problems.

I dont have that board but im quite sure thats the case.. please correct me if im wrong someone.. dont think i am tho.

 

[Heidfirst]

Intel's quoted CPU bus speed is actually 4x the real bus frequency (it's quad pumped).
DDR2 is double data rate so it's quoted speed is twice the real bus speed e.g. DDR2 800 really runs at 400MHz.
Putting it all together:
with a 1333fsb (333x4) CPU you need to run your RAM at DDR2 667 (333x2) if using a 1:1 CPU:RAM ratio.
Of course you can run the RAM faster using a ratio like 4:5 etc.

According to Intel specs. the P35 chipset only supports DDR2 800 (highest DDR2 JEDEC spec that exists) but in reality it can handle far higher - over 1200 with the right RAM & mobo.

 

[NoelS]

millz,

If you have a copy of the P5K-E User Manual, go to page 2-13. It shows a chart for FSBs of 1333 and 1066. For each of those FSBs, the BIOS will support memory timings of 1066, 800 or 667. So if your CPU is running at 1333, it will support memory at 667, 800 or 1066 MHz. One number is the CPU's FSB, the other is memory timing. A footnote says if you install 1066 memory, make sure the DRAM frequency in the BIOS's Jumperfree Configuration is set to [DDR2-1066MHz]. Otherwise it will default to 800MHz.

Noel