Chapter 2. System structure and design 33
Draft Document for Review April 7, 2004 6:15 pm 6947ch02.fm
availability purposes. Reports from the CHPID Mapping tool can help you validate your I/O
configuration.
Book upgrades with substantial additions of I/O cards may require the additional STIs to be
used. In that case it is good practice to consider rebalancing the STI configuration (FC 2400).
More information about I/O balancing, see “Balancing I/O connections” on page79. Be aware
that rebalancing of the STI configuration as a result of the addition of one or more books is
disruptive.

Book replacement and connectivity

When a book must be replaced, for example due to an unlikely MCM failure, the MBA/STIs
connectors from the failing book are unavailable. Until the failing book is replaced, Power-On
Reset of the CPC with the remaining books is not supported.
2.1.6 Frames and cages
The z990 frames are enclosures built to Electronic Industry Association (EIA) standards. The
z990 server always has two frames that are composed of two 40 EIA frames. The A and Z
frames are bolted together and have two cage positions (top and bottom).
򐂰Frame A has the CEC cage at the top and I/O cage 1 at the bottom.
򐂰Frame Z can be one of the following configurations:
– Without I/O cage.
– With one I/O cage (I/O cage 2 at the bottom).
– With two I/O cages (I/O cage 2 at the bottom and I/O cage 3 on top).
All books, the DCAs for the books, and the cooling components are located in the CEC cage
in the top half of the A-frame of the z990. In Figure2-9 on page 33 the arrows point to the
front view of the CEC cage in which four books are shown as being installed.
.
Figure 2-9 CEC cage and I/O cage locations
Z frame
MDA MDA
MDA MDA
IBF
IBF
MDA
A frame
MRU MRU
MDA MDA
MDA
IBF
BPD
CEC Cage
I/O Cage 1I/O Cage 2
I/O Cage 3