OT? Upper limits of FSB

[Peter Corlett]

On Sat, Jan 05, 2019 at 02:02:35AM -0500, Jeffrey S. Worley via cctalk wrote:
> [...] 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? [...]

Yes to both questions.

High-speed computer systems no longer resemble the simple diagrams in computer
science textbooks where there is a CPU with a parallel bus attached to memory
and I/O devices like it's still the 1970s. Sadly, the speed of light has
stubbornly failed to increase in line with Moore's Law, so we've had to reduce
the length of busses instead.

The PC's front-side-bus *was* such a 1970s-style bus, however by the 2000s it
had withered from an 8MHz bus snaking all over the board and into and out of
ISA cards to a few hundred MHz between just the CPU and the northbridge. To go
faster still, the northbridge's functionality moved on-die and the FSB is now
ancient history. (If antiquity means "before 2010".)

In general, we don't bother with parallel busses any more, just point-to-point
self-clocked serial links which can run into the gigahertz range. The bandwidth
is increased further if necessary by adding more links, but this is not the
same as a parallel bus as each link has its own independent clock and that adds
a lot of extra complexity to the receiver.