OT? Upper limits of FSB

[Jeffrey S. Worley]

Apropos of nothing, I've been confuse for some time regarding maximum
clock rates for local bus.

My admittedly old information, which comes from the 3rd ed. of "High
Performance Computer Architecture", a course I audited, indicates a
maximum speed on the order of 1ghz for very very short trace lengths.

Late model computers boast multi-hundred to multi gigahertz fsb's.  Am
I wrong in thinking this is an aggregate of several serial lines
running at 1 to 200mhz?  No straight answer has presented on searches
online.

So here's the question.  Is maximum fsb on standard, non-optical bus
still limited to a maximum of a couple of hundred megahertz, or did
something happen in the last decade or two that changed things
dramatically?  I understand, at least think I do, that these
ridiculously high frequency claims would not survive capacitance issues
and RFI issues. When my brother claimed a 3.2ghz bus speed for his
machine I just told him that was wrong, impossible for practical
purposes, that it had to be an aggregate figure, a 'Pentium rating'
sort of number rather than the actual clock speed.  I envision
switching bus tech akin to present networking, paralleled to sidestep
the limit while keeping pin and trace counts low.....?  Something like
the PCIe 'lane' scheme in present use?  This is surmise based on my own
experience.

When I was current, the way out of this limitation was fiber-optics for
the bus.  This was used in supercomputing and allowed interconnects of
longer length at ridiculous speeds.

Thanks for allowing me to entertain this question.  Though it is not
specifically a classic computer question, it does relate to development
and history.



Best,

Technoid Mutant (Jeff Worley)