This article provides information on the four PCI expansion slots contained within the Power Macintosh G3.

The Power Macintosh G3 has four PCI slots. There are actually two different PCI busses on the computer; they are:

1 - 66 MHz PCI Bus with one PCI Slot which accepts a 66 MHz 32-bit PCI card.
1 - 33 MHz PCI Bus with three PCI Slots which accept 33 MHz 32-bit or 64-bit cards.

The 66 Mhz PCI bus includes slot #1, which accommodates only 66 MHz 32-bit PCI cards. However, this slot is always configured from Apple with an Apple 2D/3D accelerated graphics card.

The 33 MHz PCI bus includes slots #2, #3, and #4, which accommodate both 32-bit and 64-bit 33 MHz PCI cards. These slots accept standard 7-inch and 12-inch PCI cards.

Some rules to remember about these slots:

• The 66 MHz PCI slot accepts only 66 MHz cards. The slot is keyed differently than 33 MHz cards and does not have the extra long slot for 64-bit cards.
• The 33 MHz PCI slots (3 of them) accepts only 33 MHz cards (not 66). These slots are longer than previous PCI slots to accommodate 64-bit cards. Older PCI cards work in these slots even though the extra section of the slot is not used.
• You can use the three 33 MHz expansion slots to install:
  three 15 W cards
  one 15 W or 25 W card
  two 15 W or 25 W cards
  one 15 W card and one 25 W card
  
  The illustration below shows the card differences between these slots. Note that key for the 66 MHz slot is located in a different place than other slots. The key is the slot which is cut into a PCI card. The key is shown below as the white gap between the gray parallel lines. The leading edge of slot is where the end of the card would be, facing the rear of the computer.