QUESTION:
Why is the speed of the CPU on board Pathfinder limited to 2.5, 5, 10, and
20 MegaHertz?

ANSWER from Lloyd Keith:
The speed of the Pathfinder computer is limited by the clock oscillator
speed. The clock is divided down by 2s to get the next lower increment,
hence the speeds of 2.5, 5, 10, and 20. We can't run slower than 2.5 MHz
because we can't service the refresh rate on the 128 MBytes of DRAM and
still have enough CPU to do useful work. During tests (with an external
oscillator that can be minutely adjusted) we have tested the CPU at 2.5 to
over 25 MHz in increments of less than 0.1 MHz.

--Lloyd Keith, MFC Chief Engineer