FSB holes, why?

[VirtualLarry]

Why, in this day and age, are there still "FSB holes" - FSB frequencies within which lead to a non-booting condition. Aren't clock generator chips linear in terms of frequency ranges?

And even if these issues used to be a problem in the past, why haven't motherboard engineers figured out a way around the issue?

 

[cprince]

It's not as simple as you think. High frequencies introduces parasitic capacitances, cross talk, etc.

 

[VirtualLarry]

Originally posted by: cprince
It's not as simple as you think. High frequencies introduces parasitic capacitances, cross talk, etc.

I understand that those could cause a max freq limitations, but why would those affect only certain frequency ranges and not others. IOW, why wouldn't those effects be linear WRT freqency?

 

[BladeVenom]

I thought it was about timings and strap.

 

[Idontcare]

Originally posted by: VirtualLarry

Originally posted by: cprince
It's not as simple as you think. High frequencies introduces parasitic capacitances, cross talk, etc.

I understand that those could cause a max freq limitations, but why would those affect only certain frequency ranges and not others. IOW, why wouldn't those effects be linear WRT freqency?

Harmonics? Constructive and destructive interferrence situations as 100's of EMF sources across the board come into play.

You could argue there is a max freq limitation which system stability scales to...it is the max frequency after which harmonic distortions will casuse FSB holes...and that is why not everyone has identical FSB holes. Their systems scaled to a different max before experiencing instability.

 

[Smartazz]

whoa, first time I've ever heard of this. This could explain a lot with my system currently. So if I set it to 265MHz, as opposed to 266MHz it might cause problems?

 

[soydios]

No, it's more that my P5W-DH doesn't like 395MHz FSB, but is fine with 401.

 

[VirtualLarry]

It just seems to me, that with certain freqencies (divisors, chipset straps, etc.), the system board overall runs outside specifications, that's why it doesn't boot. So why can't motherboard designers engineer a board that doesn't run outside of specifications, for an entire set of CPU FSB frequencies, up to some engineered max value.