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PCI Expansion Slots

The logic board uses the industry-standard peripheral component interconnect (PCI) bus for an I/O expansion bus. The Power Macintosh G3 has a primary 66 MHz bus and a secondary 33 MHz PCI bus. The 66 MHz bus is a 32-bit multiplexed address and data bus. The 33 MHz bus is a 64-bit multiplexed address and data bus.

The primary PCI bus includes slot 1, which accommodates only 32-bit 66 MHz +3.3 V PCI cards. Slot 1 conforms to the PCI V2.1 specification with the exception that its clock speed is fixed at 66 MHz so it does not accept 33 MHz cards.

The Power Macintosh G3 computer is always configured with an Apple 2D/3D accelerated graphics card installed in slot 1, so that slot is not available for PCI card expansion unless the card is removed. Slot 1 is keyed for 3.3V only operation, so older 5V cards cannot be installed in that slot.

The secondary PCI bus includes slots 2, 3, and 4, which accommodate both 32-bit and 64-bit 33 MHz +5V PCI cards.

The logic board accepts standard 6.88-inch and 12.283-inch PCI cards as defined by the PCI Local Bus Specification , Revision 2.1. The cards are required to use the standard ISA fence described in the specification.

The PCI slots support all the required PCI signals and certain optional PCI signals. The three 33 MHz PCI slots on the logic board support the optional 64-bit bus extension signals and cache support signals.

For more information about the PCI expansion slot, refer to Designing PCI Cards and Drivers for Power Macintosh Computers.