On Thu, 26 Dec 2013 14:25:10 -0600, Mark Lloyd
wrote:

On 12/26/2013 10:39 AM, Dan Espen wrote:

[snip]

I suppose serial ports have their advantages,
they're used even for disk (Sata). Probably their simplicity.

PCI Express is serial.

Apparently there's a problem with parallel at really high speeds. It
becomes impossible to guarantee that all bits are present during the
increasingly narrow window.

Exactly correct. Even very high speed "parallel" busses will have
many clocks such that not as many bits have to make it within the
narrow clock window. Others will measure the delay on each data
channel so the delay on each channel can be "normalized", so they can
all reach the destination at the same time. Serial is much easier.
The clock is even encoded in the data so there is no "skew" even
between the clock and the one bit.