James Of Tucson wrote:

At one time, the GPCs were based on a Motorola 68000, but a special
one that was designed for the space program.
That one ran OS-9. It was actually the second generation GPC, in
84.

No. The GPCs have always been from the IBM AP-101 family. They started
out as AP-101B and were upgraded to AP-101S starting in 1991. The S has
more memory and has the IOP integrated into the CPU, while the B had
separate CPUs and IOPs.

The AP-101 family never used Motorola microprocessors. The AP-101 is
binary-compatible with the IBM System/360 series.

The OS on the shuttle AP-101 GPCs has never been OS-9. The PASS GPCs run
a custom OS called FCOS. I don't remember what the OS is called on the
BFS GPC but it wasn't OS-9.

See Jenkins, 3rd ed, pp 406-407 for discussion.