FSB? Ram speed?

I'm just starting to burn in my cpu (a 2.4c) and am still abit confused about the relationship of the FSB to the memory speed. Does raising the FSB (currently @ 4x230) affect the memory (currently set to 400Mhz)? SiSoft Sandra reports the memory as running @ 2x230 (460) instead of the 2x200 (400) that the bios is set at and reports upon boot-up. I'm mainly going after the highest cpu fsb speed I can attain, and will basically leave the memory at or near stock settings (currently Crucial ram, CL3, 4-4-8-8), but have noticed that running @ 400MHz ram sometimes causes boot-up problems, but Windows runs fine. Not sure why though as the ram is PC3200 and I'm running such conservative settings.

Raising the FSB will raise the speed for everything which is why it's recommended instead of just raising the multiplyer. You may have to "relax" your memory settings or up the voltage to get it to run at the FSB you want.

The memory clock, like most others in the PC is derived from the fsb rate. Since the fsb is running at 230MHz in your case and you have the "400MHz" setting chosen in the bios you are actually running it at the 460MHz Sandra reports. The 400MHz setting is only 400MHz if the fsb is at the default 200. The setting should be labled 1:1, as when it is selected the memory base frequency is the same as the fsb's.

The fsb is quad pumped giving an effective 800MHz througput, but in reality is only running 200MHz. It is just capable of transfering 4 times as much data per clock cycle than a single pumped bus. In similar fashion DDR is dual-pumped, giving an effective 400MHz speed when usuing a 200fsb and the 1:1 ratio.

Raise the fsb to 230 as you have done, and the ram goes up to 460. This is way high for Crucial, which is generally not good overclocking ram. You can slow it down by selecting the "333MHz" setting, which in reality is the 5:4 mode. In this mode your 230fsb would be used to derive a 184MHz base memory frequency (368MHz DDR) - 230x4/5 => 184MHz. This will cost system performance but will allow greater fsb's to be achieved should your cpu be so capable. If you can gain enough cpu speed this way the system will end up faster, if only a little bit is gained it may be slower.

Ahhh... very well put larva. I figured the board was designed to lock the memory speed at whatever setting I choose just like it does the AGP/PCI bus. I didn't think the FSB would affect the mem speed, especially since the Bios on boot-up reports 400Mhz for the mem. Guess its just stating what its set at and not really what its running at.

And no wonder the 320 setting (no 333 @ 800fsb) didn't give any problems what so ever. But hey, 2 days laters I'm still here crunching away at Seti with the ram @ 460.

The only problems it give with the mem at this speed is when I re-boot XP, it sometimes hangs or resets after the XP boot screen. Other then that, once in XP, all seems to run fine.

But I will have to bring it back down to 320 if I want to make 3.0G on the cpu.

Yeah, I forgot they label it 320 instead of 333. It is of course 320 with 5:4 at 200fsb. The setting is intended for the use of 333MHz DDR, but of course the simple ratios don't land right at that frequency.

Chances are in your case the 320, or 5:4 setting will be productive as it should allow you raise your fsb (and hence the cpu rate) quite a bit. It sounds like it isn't 100 percent stable at 460 on the memory anyway, so I 'd definately work in that direction.

Mpegger said:

I'm mainly going after the highest cpu fsb speed I can attain, and will basically leave the memory at or near stock settings

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Your fsb doesn't matter to your CPU, unless you have locked multi's of course. I dunno, I use AMD.