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CHAPTER 11: ADVANCED USERS
11.4 BACKPLANE SLOT ORDERING
The order in which the System BIOS enumerates the cards is dictated by the way the PCI Express slots are mapped onto the PCI
Express switch on the backplane. Unfortunately, this is dictated by the routing of the tracks from the slot to the switch on the
backplane. The track routing is designed to provide the highest signal integrity possible, and this means that there is not necessarily
a straight mapping between physical slot number and logical BIOS enumeration.
TABLE 11-4. BACKPLANE SLOT ORDERING
Physical Slot
9-Slot G3 Bus
Number
9-Slot
1
G3 Bus
Number
11-Slot G3 Bus
Number
1
1
1
3
2
2
2
2
3
3
3
7
4
4
4
6
5
5
5
11
6
6
9
10
7
7
8
9
8
8
7
8
9
9
6
5
10
--
--
4
11
--
--
1
1
This order was introduced in Revision F of the 9-slot G3 backplane. Before this, the ordering was as found in the original Express9.
The revision can be determined from the backplane serial number, and the Revision F serial number will always start with 163F.
The table shows that the first card enumerated by the BIOS when using an 9-slot G3 is the one in Slot 1. However, on an 11-slot G3,
the first card enumerated would be the card in Slot 11.
The last card enumerated in an 11-slot G3 would be the one in Slot 5. If we were using an SBC4 with this backplane, then an Im-
ageDP4 card would be programmed with the IO Enabled BIOS. Additional cards could have their IO requirement disabled. If Slot 5 is
not populated with an ImageDP4, the card that would require IO would be the one with the highest bus number.
The last slot enumerated in a 9-slot G3 by the SBC4 would be Slot 6. In the same manner as the Express11, if a VGC-DP-4
or VGC-DP-4-R2 is placed in this slot, it should be the IO enabled card.
It is also worth noting that once booted into Windows, the drivers will reorder the hardware so that it appears in the order dictated by
the jumpers on the card, or by the physical slot if the jumpers are not set. We hide the logical bus order from the user to simplify the
wiring of the inputs and outputs.
