Choosing an interface

Any device connected to your computer uses some type of interface to move data back and forth. The interface is just a physical connection - a plug, if you will. Many types of devices are sold with a choice of interfaces, and you need to know enough about the different interfaces to choose the right one for your needs.

Interfaces for adapter cards

Adapter cards (computer cards that plug straight into the PC's motherboard) use one of three types of interfaces, corresponding to the three types of slots on the motherboard. The names of the slots are pretty weird, but don't let the terminology put you off. There were reasons for the names, once upon a time, but they don't really mean much nowadays.

The PCI interface gets the nod for most adapter cards. It's physically strong (so you'll have a hard time breaking the sucker when you stick a card in the slot), and lots of electrical contacts are inside. PCI supports Plug and Play operation, which means that Windows XP can detect the properties of an adapter card and do much or all of the software installation automatically. Most Windows computers have three, four, or five PCI slots.

The AGP interface is for video adapter cards only - that is, cards that slap stuff up on your screen. An AGP slot is shorter than a PCI slot. Some AGP slots have a little lever that flips up on the back to hold the card in tighter. Video adapters with the AGP interface can offer better performance than those with the PCI interface. AGP is also a plug-and-play interface.

Warning Not all Windows PCs have separate AGP slots, so check before you buy an AGP card, okay? An AGP card without an AGP slot is about as useless as a kite without a string.

The ISA interface is a much older interface, and it's not Plug and Play. Most modern Windows computers have just one ISA slot or none at all.

Warning Do not buy an adapter card with an ISA interface unless you need something unusual that is only made that way. If you buy an ISA card, expect to spend lots of hours wrestling with arcane topics such as IRQs, DMA channels, and base I/O addresses - all three of which were government plots designed to keep computers out of the hands of "normal" people. You have a hard time finding ISA cards nowadays for a reason. Let them die a well-deserved death.