Compaq GS160 - Manual (Page 143)

Using the System Control Manager 8-3
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.