2.2 AirPort Cards
| All of the computers that Apple has manufactured since 2000 are AirPort-ready , meaning that they contain an internal slot that can accept either an AirPort card or an AirPort Extreme card. These cards are the radio transceivers that transmit and receive the Wi-Fi signals. PowerBooks, iBooks, iMacs, eMacs, and Power Macintosh G4 desktops have internal antennas in their cases that plug into the cards. The all-aluminum case of the Power Macintosh G5 computers prevent the transmission of radio signals through the case, so these machines come with a small external AirPort antenna that plugs into the computer's rear panel. 2.2.1 The Original AirPort CardThe original AirPort card supports the 802.11b standard, for theoretical data transfer rates of up to 11 Mbps. In the real world, however, signal inefficiencies and networking overhead reduce the actual data throughput you'll get from 802.11b to approximately 6 Mbps at best, which is still plenty fast for Internet surfing and most network file transfers. Distance is also a factor with wireless: that 11 Mbps figure is for throughput close to the base station. As you get farther away, the signal will degrade to 5.5 Mbps, then 2 Mbps, 1 Mbps, and 512 Kbps before you lose the signal altogether. The AirPort card is a special version of a PC card, similar to the cards used in the expansion slots of notebook computers such as Apple's PowerBooks. The card has a 16-bit interface running at 10 MHz, with an effective data throughput of approximately 20 Mbps. However, the AirPort card is specifically designed for the internal slots used in Apple's machines, and can't be used in regular PC card slots. Figure 2-3 shows the AirPort card. Figure 2-3. The AirPort card supports only 802.11b Table 2-2 lists the computers compatible with the AirPort card, with the annoyingly vague and nondescriptive terminology that Apple uses for each model. Table 2-2. AirPort-ready Macintosh computers
The $79 AirPort card is still available from Apple for use with the Macintoshes listed in the table. Newer Macs use the AirPort Extreme card. 2.2.2 The AirPort Extreme CardBesides supporting the 802.11g standard, the $99 AirPort Extreme card is quite different from the older AirPort card. For one thing, it's physically much smaller; as Apple says, it's about half the size of a standard business card. The change in the card's form factor was necessary to support 802.11g's higher speeds. The AirPort Extreme card is a Mini-PCI card that connects to a full-speed PCI bus in AirPort Extreme-ready computers. This is a full 32-bit PCI 2.2 bus running at 33 MHz, offering throughput of around one gigabit per second. That's more than fast enough to handle 802.11g's rated 54 Mbps speed, and easily handles its effective 25 Mbps throughput. Figure 2-4 shows the AirPort Extreme card. Figure 2-4. The AirPort Extreme card AirPort Extreme's need for the Mini PCI bus is the reason there can't be an AirPort Extreme card for older AirPort-enabled systems; the AirPort slot for those systems, running at only 10 MHz, simply can't transfer the data fast enough. AirPort Extreme was introduced in January 2003, and most new Macs announced since that date use AirPort Extreme, rather than AirPort. Table 2-3 lists Apple's AirPort Extreme-ready Macintoshes. Table 2-3. AirPort Extreme-ready Macintosh computers
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