Compaq AlphaServer GS80 User Manual page 141

The SCM communicates with the PCI backplane managers (PBMs), the
hierarchical switch power manager (HPM), and the QBB power system
managers (PSMs) distributed throughout the CSB subsystem. The subsystem
has a power source separate from the rest of the system called auxiliary voltage
(Vaux). Vaux enables the subsystem to be turned on from a remote site when
the main system breaker is on and the system is plugged in.
Using the System Control Manager 8-3