Compaq GS160 - Manual (Page 30)

2-12 AlphaServer GS80/160/320 User's Guide
2.3.4 Directory Module
In a GS160/320 system, one directory module is required for each QBB
in a system box. In a two-drawer GS80 system, a directory module is
required in each system drawer. No directory module is needed in a
one-drawer system.
The directory module functions as a memory
coherency manager.
Figure 2–8 Directory Module
Directory
DIMMs
PK0606