Potential source of interrupt aliasing

[Danny Braniss]

...
> It's a pity that the modern PC is hamstrung by design decisions made
> over 25 years ago.

sorry, but couldn't help it :-)

The US Standard railroad gauge (distance between the  rails) is 4
feet, 8.5 inches. That's an exceedingly odd number.  Why was that
gauge  used?   Because that's the way they built them in England,
and the US railroads were built by English expatriates.

Why did the  English people build them like that?

Because the first rail lines were  built by the same  people  who
built  the pre-railroad tramways, and that's the gauge they used.
Why did "they" use that gauge   then?   Because  the  people  who
built  the  tramways  used the same jigs and tools that they used
for building wagons, which used that wheel  spacing.   Okay!  Why
did  the  wagons use that odd wheel spacing?  Well, if they tried
to use any other spacing the wagons would break on  some  of  the
old,  long  distance roads, because that's the spacing of the old
wheel ruts.

So who built these old rutted roads?

The first long distance roads in Europe were  built  by  Imperial
Rome  for  the benefit of their legions. The roads have been used
ever since.  And the ruts?

The initial ruts, which everyone else had to match  for  fear  of
destroying  their  wagons, were first made by Roman war chariots.
Since the chariots were made for or by Imperial  Rome  they  were
all  alike  in  the  matter  of  wheel spacing. Thus, we have the
answer to the  original  question.  The  United  States  standard
railroad  gauge  of  4 feet, 8.5 inches derives from the original
specification for an Imperial Roman army war chariot.  Specs  and
Bureaucracies  live  forever.  So, the next time you are handed a
spec ification and wonder what horse's ass came up with  it,  you
may  be  exactly right.  Because the Imperial Roman chariots were
made to be just wide enough to accommodate the back ends  of  two
war horses.

Now the twist to the story....

There's  an  interesting  extension  of  the story about railroad
gauge and horses' behinds.  When we see a Space  Shuttle  sitting
on  the launch pad, there are two big booster rockets attached to
the sides of the main fuel tank.   These  are  the  solid  rocket
boosters,  or SRBs.  The SRBs are made by Thiokol at a factory in
Utah.  The engineers who designed the SRBs might  have  preferred
to  make  them  a  bit  fatter, but the SRBs had to be shipped by
train from the factory to the launch site. The railroad  line  to
the factory runs through a tunnel in the mountains.  The SRBs had
to fit through that tunnel.  The tunnel is slightly wider than  a
railroad  track,  and  the railroad track is about as wide as two
horses' behinds.  So a major design feature of what  is  arguably
the world's most advanced transportation system was determined by
the width of a horse's ass!