Nobody really remembers what BUP stands for. I was told that it stood for Bring Up Program. If this is true, it's a misnomer. By the time the machine was in bring-up, the BUPs had already run successfully in simulation and found all the problems they were likely to find.

Bring Up
The period of hardware debug when a real machine is available.

The period of hardware debug when the machine exists only as a software model. Simulators run several orders of magnitude slower than real machines.