IBM 990 - Manual (Page 45)

Chapter 2. System structure and design 33
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 a good practice to consider rebalancing the STI configuration (FC
2400). For more information about I/O balancing, see 3.2.3, “Balancing I/O connections” on
page 79. 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 Figure 2-9, 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 1 I/O Cage 2
I/O Cage 3