PCI Bus Numbering in a Microsoft Windows NT Environment

PCI Bus Numbering in a Microsoft Windows NT Environment 21
13UK-1200A-WWEN
Note: Even though PCI bus numbers assign during every boot process, the number remains
exactly the same as long as the configuration remains the same.
Table 6. PCI BIOS bus detection in a ProLiant ML530–before adding a bridged controller
Bus
Detection
Order/
Controller
Discovery
Slot
Number
PCI Bridge/
Controller
Type – Test 1
Bus Number
Assignment
Description of PCI BIOS Discovery
Process
1st
Primary
Bus (O)
Host to PCI
Bridge
Bus 0
2nd Slot 1 Empty N/A
3rd
Secondary
Bus (2)
Host to PCI
Bridge
Bus 2
4th Slot 7 Empty N/A
5th Slot 8 Empty N/A
6th
Tertiary
Bus (5)
Host to PCI
Bridge
Bus 5
7th Slot 6 Empty N/A
8th Slot 4 Empty N/A
9
th
Slot 3 Empty N/A
10th Slot 2 Empty N/A
11th Slot 5 NC3132 (non-
bridged)
Bus 5
The PCI BIOS discovers the Primary Bus
and assigns it bus 0.
Discovery process continues to PCI slot 1.
No PCI controller detected, no bus number
assigned.
The PCI BIOS discovers the Secondary
Bus and increments the bus number to 2.
Discovery process continues to PCI slot 7.
No PCI controller detected, no bus number
assigned.
Discovery process continues to PCI slot 8.
No PCI controller detected, no bus number
assigned.
The PCI BIOS discovers the Tertiary Bus
and increments the bus number to 5.
Discovery process continues to PCI slots
6, 4, 3, and 2. No PCI controller detected,
no bus number assigned.
PCI BIOS detects a NIC (no PCI bridge) in
slot 5, it is assigned the same bus number
as the PCI Bus where it resides, and is the
first controller detected by the PCI BIOS.
Reviewing the Test 1 Configuration
In Test 1, the PCI BIOS begins the discovery process by identifying buses on the Primary PCI
Bus, then continues to the Secondary PCI Bus looking for PCI buses and or bridges, and
completes after reaching the last slot on the Tertiary PCI bus. As each bus is detected it is
assigned a bus number starting at bus 0, the PCI BIOS then assigns bus numbers to the PCI
controllers discovered on each bus. In this example, the controllers do not contain bridges.
Therefore, they are assigned the same bus number as the bus on which they reside.
Note: Bus numbers (appear in boldface type in Table 6) are assigned during bus initialization
according to predefined hardware designators. The bus numbers may not appear to follow a set
increment and some numbers may be skipped. However, by this method, these hardware
designators prevent overlays in bus numbering from occurring.