Compaq GS160 - Manual (Page 39)

GS160/320 System Overview 2-21
The hierarchical switch links the QBBs in systems having more than one
system box. Figure 2–16 shows cable connectors for each system box (a pair of
connectors for two signal cables routed to each QBB global port in the system).
The hierarchical switch power manager (HPM) module controls power and
monitors the temperature inside the hierarchical switch housing. The HPM
module, along with the PSM modules and PBM modules, report status
information to the SCM.