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If you have a modular desktop Power Mac or Performa (most models), or a Mac clone built since late 1995, with a 603, 604, G3, or G4 processor, your machine has a Peripheral Component Interconnect (PCI) expansion bus, which allows you to expand and upgrade the computer's capabilities using easy to install, plug-in, expansion cards. (Cubes, and some Performas, are an exception, as are the non-modular iMacs and Apple portables, all of which have had PCI motherboard architecture since 1995, but have no PCI expansion slots).

For example, if you have an older PCI Mac (running OS 8.6 or later) that doesn't support USB or FireWire connectivity, you can easily upgrade to either or both by adding a relatively expensive PCI card or cards (combination USB/FireWire cards are available). Other types of PCI cards include video boards, Ethernet cards, ATI/IDE controllers for using IDE drives in SCSI Macs, SCSI support on IDE Macs, video capture cards, and others.

PCI cards are either 7 in. or 12 in. expansion circuit boards with male slot connectors and usually a port or set of ports that face through an aperture in the back of the computer's case. If your Mac is PCI upgradable, it will have a row of two to six PCI slots located at the back of the motherboard. Installing a PCI card is essentially just a matter of plugging the card into one of the slots.

If you are capable of and comfortable with opening up your computer, you should be able to install a PCI card with little difficulty. If you have ever installed a RAM upgrade, you should find installing a PCI card no more difficult, and in some cases easier. How to open up various Macs and clones is beyond the scope of this article, and can range in difficulty from very easy to a moderate pain. Check your owner's manual for instructions pertaining to your particular machine.

In general, turn off the Mac. There are two schools of thought as to whether you should leave the power cord plugged in (for grounding purposes). You can make your own evaluation about that. It's a good idea to let the Mac sit unpowered for half an hour or so to allow various capacitors to discharge before getting to work, although I don't know anyone who actually does this. A grounded wrist strap is also a good idea as a precaution against static discharge damaging your computer's internal components.

Once the Mac is open, also touch the power supply case (the internal module into which the power cord plugs) to discharge static electricity from your body.

If your PCI card has external ports (most do), you will need to remove the case aperture blanking plate next to the slot you plan to use, in order to allow the card's ports to protrude through the case. This usually involves removing just one screw and lifting the blanking plate out. Some plates are secured by clips rather than a screw. Save the plate in case you decide to remove the PCI card in future.

Remove the PCI card from its packaging and/or anti-static beg. Hold it by its edges, or by the metal port face plate. Orient the card over the PCI slots so that the ports, if present, face through the case aperture, and gently press the card's connector into the slot. It should slide "home" with reasonable pressure. Don't use excess of force if it resists; it's probably misaligned. Once the card is seated properly in the PCI slot, you usually secure it with the screw you removed from the case aperture blanking plate.

Now, before closing the case, boot up the Mac to make sure everything is working fine. If all goes well, shut it down again, close up the case, and the hardware installation is finished.

That may be all you need to do, although in some cases, you may also need to install software drivers to support the card. Check the instructions that came with your PCI card for software installation details, if applicable.