These look like [PCMCIA] cards but actually aren't. They are used to upgrade "AirPort ready" Apple computers (both desktop and laptop) with wireless capability. Apple's [AppleAirport AirPort Base Stations] are standard 802.11b so AirPort Card equipped Apples will work with non-Apple access points and vice versa.

{http://store.apple.com/Catalog/Australia/Images/top3_airport_card.jpg Airport card}

The special AirPort connector on AirPort-ready Apples carries an antenna pin, which connects to an antenna built into the frame of the machine.

AirPort-ready, G3-based, slot-load iMacs need a caddy to install an AirPort card.