Dell PowerVault 775N (Rackmount NAS Appliance) - Manual (Page 46)

Expansion Cards
The system includes three expansion slots. The expansion cards are installed on the system's riser board (see Figure 5-4 to
identify the expansion slots).
Expansion Card Installation Guidelines
You can install expansion cards of different operating speeds on the same bus; however, the bus will operate at the slowest
operating speed of the cards on that bus. For example, if one card on the bus has an operating speed of 66 MHz and the
other card has an operating speed of 100 MHz, the bus will only operate at 66 MHz.
To identify expansion slots and PCI buses, see Figure 5-4 . Table 4-1 lists the PCI bus and operating speed for each
expansion-card slot.
Table 4-1. Expansion Slot Speeds
Slot Bus Operating Speed
1 1 33, 66, or 100 MHz
2 1 Slot 1 is not empty — 33, 66, or 100 MHz
Slot 1 is empty — 33, 66, 100, or 133 MHz
3 2 33, 66, 100, or 133 MHz
NOTE: If you are using expansion cards of different operating speeds, you should install the fastest card in slot 3 and the
slowest card in slot 1.
PCI Bus Scan Order
The system's BIOS scans and numbers PCI buses and devices during startup. Expansion slots are scanned according to the
host bus ordering, not by the slot numbers. See Table 4-2 for the order in which the expansion slots and integrated PCI
devices are scanned. Figure 5-4 provides a diagram of buses and expansion slots.
An additional factor affects the assignment of PCI bus numbers: an expansion card may have its own PCI bridge chip which
requires the assignment of a bus number for the card as well as one for the bridge. A particular expansion card may have two
PCI bridge chips which would result in three sequential PCI bus numbers all assigned in the same expansion slot.
If you install expansion cards, you may have some difficulty in directly determining the bus number of a controller on a
particular expansion card. However, the PCI bus scan order listed in Table 4-2 can help determine the relative numbering of
PCI buses within the expansion slots. For example, a PCI controller residing in expansion slot 3 will never have a lower bus
number than one in slot 2 because slot 2 precedes slot 3 in the scan order.
Table 4-2. PCI Bus Scan Order
Order Device or Slot
1 Video
2 Embedded remote access components
3 Expansion slot 1
4 Expansion slot 2
5 Expansion slot 3
6 Integrated NIC 1
7 Integrated NIC 2
8 Integrated SCSI controller on the system board
9 Integrated RAID controller on the system board