IBM 990 - Manual (Page 89)

Chapter 3. I/O system structure 77
Each eSTI-M card is connected to an STI jack located in a book’s Memory Bus Adapter
(MBA) via an STI cable. As each eSTI-M card requires one STI, up to seven STIs are
required to support one I/O cage. A fully populated three-I/O cage system requires 21 STIs.
IBM selects which slots are used for I/O cards and supplies the appropriate number of I/O
cages and STI cables, either for a new build server or for an existing server upgrade.
3.2.1 Self-Timed Interconnect (STI)
There are three Memory Bus Adapters (MBAs) on each z990 book. Each MBA has four
Self-Timed Interconnects (STIs), resulting in a total of 12 STIs on each z990 book. Each STI
has a bandwidth of 2 GBps full-duplex, resulting in a maximum bandwidth of 24 GBps per
z990 book.
Depending on the number of books in the configuration, there will be 12, 24, 36, or 48 STIs in
a z990 server, as shown in Table 3-2.
Table 3-2 Number of MBAs and STIs
The z990 model D32 has a maximum bandwidth of 96 GBps.
3.2.2 STIs and I/O cage connections
Figure 3-3 on page 78 shows the STI connections from the server’s CEC cage to an I/O cage,
and to an Integrated Cluster Bus-4 (ICB-4) link.
5 20, 22, 25, 27
6 29, 30, 31, 32
Important: Installing an additional I/O cage to an existing z990 server configuration is
disruptive. The Plan Ahead process allows you to avoid this outage by including, in the
initial z990 server order, the number of optional I/O cages required by a future I/O
configuration.
Domain I/O slots in domain
z990 Model Number of books Number of MBAs Number of STIs
2084-A08 1 3 12
2084-B16 2 6 24
2084-C24 3 9 36
2084-D32 4 12 48