Problem Determination Guide - Systems Group

1.2.8 Clock card
The clock card is attached physically to the bottom of the rack and is connected
to the midplanes in the system through special cables that connect to the coaxial
ports that are located on the front of each service card (Figure 1-13). Because
Blue Gene/L is a massive parallel system, the clocks on all nodes that are
involved in running a job must be synchronized (especially for any MPI job). The
clock card logic provides the necessary synchronization for all node cards.
Figure 1-13 Clock card
1.2.9 Bulk power modules/enclosure
The bulk power modules (BPM) are located on top of each rack. There are seven
modules per rack (three in the front and four in the back of the rack). These
modules are connected in an n+1 redundancy scheme. The modules are
inserted into the bulk power enclosure (BPE), as shown in Figure 1-14, which
also houses the circuit breaker module that is used to turn on and off the rack.
Figure 1-14 Front view of the BPE (three BPMs and a circuit breaker)
Chapter 1. Introduction 15