Service manual

System Overview 1-7
Figure 1–3 shows the rear view of a system box. Each CPU and each memory
module is assigned a physical ID associated with the slot in the QBB backplane
in which it resides. A GS320 system can have up to four system boxes each
with two QBBs. When all QBBs contain the maximum of four CPUs, a system
containing 32 processors is created.
Global ports must be physically close to each other and to the hierarchical
switch and therefore are connected either to the front of a QBB backplane or to
the back. The global port module attached to the front backplane is plugged
into its back. And the global port module attached to the back backplane is
plugged into its front. The global port module attached to the front backplane
extends to the rear of the system box though the cutout in the rear backplane.
The two backplanes in the system box are oriented so that the global port
connector on the front backplane is opposite the cutout in the rear backplane.
See Figure 1–2.