Does memory speed have to match the fsb?

[Cancer12]

I'm doing one of my periodic upgrades, and this is puzzling me. Does the cpu fsb and the memory speed have to match? I know that this used to be true, but it seems like the opposite now. If I get a E8400, which is 1333fsb, do I need to get the matching ddr2667 memory? Or would the memory not run at that speed anyway? This system won't have any overclocking done on it, so extra headroom doesnt matter.

The reason I'm confused is because the Gigabyte board I'm looking at has 1333fsb listed, but then the max memory speed only goes up to 1066. Does that mean its very normal these days for the cpu and memory to run out of sync? Does it kill performance?

Answers to these questions or pointing me to a refresher sort of guide will earn you many cookies. Thanks

 

[Blain]

1333MHz FSB = DDR2 667
Easy way to remember is that Intel CPU's are "quad pumped" (x4) and DDR2 is x2.

Math > 1333 divided by 4 = 333 (in the PC world) > DDR2 667 divided by 2 = 333 (in the PC world).

If you buy DDR2 800, you will have plenty of memory speed for a 1333 CPU.

 

[Cancer12]

Yeah I realize that. My question is does the memory have to match the fsb? For example, the Gigabyte EP35 http://www.newegg.com/Product/...x?Item=N82E16813128337 has a fsb of 1333, but the highest non oc memory speed for it is 1066. Does that mean that it is expected to run the memory and fsb out of sync? Is that how everything works now?

 

[Blain]

Originally posted by: Cancer12
Yeah I realize that. My question is does the memory have to match the fsb? For example, the Gigabyte EP35 http://www.newegg.com/Product/...x?Item=N82E16813128337 has a fsb of 1333, but the highest non oc memory speed for it is 1066. Does that mean that it is expected to run the memory and fsb out of sync? Is that how everything works now?

To strictly answer your question...
No, your memory does not have to match the FSB of your CPU.

If you set DDR2 1066 1:1 with your CPU FSB, the CPU FSB would be running at a 2132.
If that sounds confusing, read some good reviews on Gigabyte P35 MBs. Basically all their BIOS memory settings are the same.

 

[betasub]

Originally posted by: Blain
If you set DDR2 1066 1:1 with your CPU FSB, the CPU FSB would be running at a 2132.
If that sounds confusing, read some good reviews on Gigabyte P35 MBs. Basically all their BIOS memory settings are the same.

Yes that sounds confusing. You make it appear that CPU FSB is based off the memory's operating speed rather than vice versa.

OP: for a P35 motherboard, the slowest the memory can run with a 1333FSB CPU is 667MHz (1:1). Other ratios are available in BIOS (AUTO will usual select from SPD info), so that memory can run faster (e.g. 800 or 1066MHz) - performance gains for most apps are typically very small (but measureable).

 

[Cancer12]

Oh ok I'm retarded. The 667ddr2 speed matches the 1333fsb. I knew that but was confused by the labeling on the mobo. Thanks