[Reason077]

It's not a Mac (in the "I know this!" scene), it's a Silicon Graphics workstation.

Although a Quadra running A/UX would have been a legitimate Unix at the time, too.

[chess_buster]

Correct, it's a SG Crimson (there's also an Indigo somewhere). But the other computers are Macintosh Quadra 700 – and 8 Connection Machines (CM5, so no XMP Cray as in the book) in the background providing the blinkenlights.