Dell OptiPlex GX1p User Manual page 34

Option 1 is a passive riser board, with no PCI-to-PCI bridge. ISA1 and PCI3 share the same card-slot opening.
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Option 2 is an active riser board, with a PCI-to-PCI bridge. ISA1 shares its card-slot opening with PCI4, and ISA2 shares its card-slot opening with PCI5.
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Mini-Tower Chassis Riser Board
ISA1 shares its card-slot opening with PCI4, and ISA2 shares its card-slot opening with PCI5. The riser board is active, incorporating PCI-to-PCI bridging.