FSB, synch vs asynch mode etc.

[Octopuss]

Hello people. I am not really a newb when it comes to overclocking, but apparently I have been slacking at keeping my knowledge up to date

So please tell me:

1) Is it only the resulting CPU frequency that matters the most, or does the FSB play any important role as well? I mean, is there any performance benefit in having say around 550 FSB over 400-450? Just this by itself - memory and CPU is a different story.

2) Does synchronous mode still matter, or do the days of 1:1 FSB:memory ratio belong into history textbooks?

 

[newconroer]

For basic overclocks, a FSB increase is usually used.
However when you get a bit more into it, you end up working backwards from the RAM, as having synched mode is generally more stable, and keeps your ratio(s) in-tact.

The problems begin when your FSB is too high to maintain a 1:1 or even 1:2 ratio.
Thus you might use a max CPU multiplier and a lower FSB.

Alternatively, some CPUs at a higher multiplier require higher voltage, to negate this, you can use a higher FSB with a lower multiplier, but then you end up back at the RAM issue.


As for performance, you won't see much difference, between higher FSB with a lower multiplier, or vice versa.


Assuming you can get away with non-linked memory, then it's pretty open range on what you want to do. Either way, the CPU voltage is a mains voltage; eventually it's going to have to be raised. I say eventually, because some chips can go pretty far on stock CPU voltage at a higher FSB, like some of the older Core 2s; but if you go just a tad over that threshold, then the voltage increase will become required, and sometimes it's not worth it.

You could get a chip that goes another 1ghz without a voltage bump, but in order to get even another stable 500mhz, you'd potentially be pushing it into a danger voltage range.

Which points to a good rule of thumb that most modern chips have this stock voltage threshold and that's about where you want to stop, to get the best performance/power draw. Unless your synethetic testing, then the performance vs. power draw isn't worth it.

 

[Octopuss]

Thanks.
I've got E8400 which can get to 3.75GHz with default VCORE, 4 with around 1.32, but I couldn't squeeze 4.2 from it even with 1.45 Damn thing.
The reason why I posted all this is that I did have a stable 540x7.5 setup with 1:1 memory, but for some reason it became unstable after a week and I couldn't get back to it even with raised NB voltage - so I am looking for alternative methods. Lower FSB needs so much less tweaking...