I/O Subsystem - Compaq AlphaServer DS20 Service Manual

1.8.2 I/O Subsystem

The I/O subsystem consists of two 64-bit PCI buses. One has an embedded ISA
bridge, three PCI option slots, and a single ISA slot; the other bus has three PCI
option slots.
Figure 1-11 PCI Block Diagram
CAP Bus (24 bits)
1 ISA
P Chip
PCI 0
Cypress Chip
(ISA Bridge,
Q8DÃ7ˆ†
IDE, KBRD,
MSE, USB)
ADAPTEC
Ultra SCSI
Controller
(2 ports)
PCI-0
3 64-bit slots
1-20 AlphaServer DS20 Service Manual
Crossbar
Switch
C Chip
8 D Chips
PAD Bus (32 bits)
Slot
I/O ASIC
COM1
COM2
Parallel
Port
P Chip
PCI 1
Floppy
PCI-1 Bus
PCI-1
3 64-bit slots
PK1494-98