cyclebabble

    Advertising raw clock speed, instead of bus
   speed.

   IBM uses raw clock speed as the speed of the computer.  In
   the IBM PC and IBM PC XT, the clock is divided by 4 to
   produce the 4-phase bus clocks.  Thus a 4 MHz IBM XT really
   runs at 0.895 MHz, because that 4 MHz was really 3.58 MHz
   which gets divided by four.

   A Tandy Color Computer ran at exactly the same speed, but
   clock speed was specified as bus speed, 0.895 MHz, leaving the
   impression that it was 4 times slower.  Actually it ran a
   little faster with a more efficient instruction set.  If the
   actual clock rate had been specified on a CoCo 3, it would
   have been 14.32 MHz, although the bus speed was still 0.895
   MHz.  That high speed also generated video, color, and hidden
   refresh timing.

   100 MHz computers are running at bus speeds of around 25 MHz.

   (1997-02-13)