1.2.2.7 Additional DSSI Buses
Your system can have up to four Digital Storage System Interconnect (DSSI)
adapters. If your system has four DSSI adapters, two are built into the CPU, and
two are installed on the DSSI bus daughter board (KFDDB), which is connected
to the CPU module. They provide a path to four separate DSSI buses (0, 1, 2, and
3) through which the CPU can communicate with DSSI devices.
Each adapter can support eight nodes, with the adapter and each DSSI storage
device counting as one node. Therefore, each adapter can support seven DSSI
storage devices.
The adapters also let you link one of the DSSI buses to another system to form
a DSSI VAXcluster configuration, described in Section 1.3. When a DSSI bus
is extended to a second system, both systems can share up to six DSSI storage
devices. When a DSSI bus is extended to a third system, the systems can share
up to five DSSI storage devices.
When your system is configured with four DSSI buses, slots 6 through 12 can be
configured in the following ways:
• Slots 6 through 10 are available for Q–bus option modules (Figure 1–1 a.).
• Slot 12 will contain an expansion module (M9404) (Figure 1–1 b.).
Slots 10 and 11 will contain DSSI bus bulkheads if there is an expansion
module in Slot 12. Slots 10 and 11 require Q–bus grant cards in this case. If
there is no expansion module in Slot 12, then Slots 12 and 11 are used. No
Q–bus grant cards are needed in this instance. (Figure 1–1 b.).
1–28 System Overview
