What is is 802.11n? How is it different from 802.11b, 802.11g, and 802.11a?

802.11n, which Apple confusingly dubs "AirPort Extreme" -- the same name given to the earlier 802.11g specification -- is a wireless networking standard supported by the Apple TV. Apple also supports 802.11n on Macs starting with the Core 2 Duo-based models (some first require enabler software to be installed) -- with the exception of the iMac "Core 2 Duo" 1.83 17-Inch (IG) -- as well as the Mac Pro models if configured with an AirPort Extreme card.

In basic terms, 802.11n is faster than 802.11g, which itself is faster than the earlier 802.11b. On the company website, Apple explains that 802.11n offers "greater performance, more range, and improved reliability". Apple also notes:

Among its key innovations, 802.11n adds technology called multiple-input multiple-output (MIMO), a signal processing and smart antenna technique for transmitting multiple data streams through multiple antennas. The result? Up to five times the performance and up to twice the range compared to the earlier 802.11g standard.

Diagram Credit: Apple, Inc.

The always excellent BareFeats evaluated the Apple AirPort Extreme 802.11n base station and found it to be "3.8 times faster than the 802.11g setup" in real-world tests. The always superb MacInTouch also reviewed the same product and found it to be substantially faster as well but also discovered a number of caveats and limitations that may effect some users.

As noted elsewhere on EveryMac.com, 802.11a formally is not supported by Apple, but all Intel-based Macs work with an 802.11a network. 802.11a offers the same theoretical speed (54 Mbps) as 802.11g, but it operates in a different frequency (5 GHz) and is not backwards compatible with 802.11b.

802.11n can operate on either the 5 GHz frequency at full speed or on the 2.4 GHz frequency in "mixed mode" which will support systems only capable of using 802.11b or 802.11g, but it will slow the entire network down to the maximum speed of the earliest standard connected.

For your convenience, the main differences between 802.11b, 802.11g, 802.11a, and 802.11n are summarized below.

Apple Product	Standard	Speed†	Range†	Frequency
AirPort	802.11b	11 Mbps	150 Feet	2.4 GHz
AirPort Extreme	802.11g	54 Mbps	50 Feet	2.4 GHz
AirPort Extreme*	802.11a	54 Mbps	50 Feet	5 GHz
AirPort Extreme	802.11n	300 Mbps	175 Feet	2.4/5 GHz

† Real-world speeds are more modest. Likewise, range varies depending on configuration and placement.
* Apple provides no official support for the 802.11a standard, but it works with all Intel-based Macs.

For a highly-technical look on 802.11n, you also may be interested in reading a DeviceForge article.