Chapter 2. System Board Features
Riser Card
The system board uses a riser card for expansion. The riser card plugs into the system board, and
adapters plug into the ISA-expansion or PCI-expansion connectors on the riser card. Signals from
adapters are routed to the ISA or PCI buses. Each ISA-expansion connector provides a 16-bit-wide data
path; each PCI-expansion connector provides a 32-bit-wide data path.
Each PCI-expansion connector is capable of driving one low-power Schottky load. Each ISA-expansion
connector is capable of driving two low-power Schottky loads. The ISA bus is permanently set to the PCI
bus speed divided by four.
The PCI bus shares interrupts with the ISA bus. IRQ 3, 5, 9, 10, or 11 is automatically assigned to PCI
adapters during POST. If no interrupts are available for the PCI adapters during POST, an error message
is generated.
One of two types of riser cards is used for expansion. Although both types of riser cards have five
expansion connectors, the number of dedicated PCI and ISA connectors varies. The following table
shows the characteristics of the two types of riser cards.
Note: The enhanced 5x5 riser card has a PCI-to-PCI bridge chip that enables the card to support five
PCI slots.
The computer comes standard with adapters plugged into the expansion slots of the riser card. For more
information, see Chapter 3, “Adapters and Internal Drives” on page 17.
For information on the connector pin assignments, see “ISA Connectors” on page 38 and “PCI Connector”
on page 40.
Table 8. Riser Card Characteristics
Expansion Connectors
5x5 Riser Card
Enhanced 5x5 Riser Card
Shared ISA/PCI
3
3
Dedicated ISA
2
0
Dedicated PCI
0
2
Chapter 2. System Board Features
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