, or multiple-input, multiple output, is probably the first thing that comes to mind when people think about what's new in 11n. It is the most visible and the most talked-about of the advanced technologies. MIMO uses complex radio frequency (RF) technology that allows multiple data streams to be transmitted over the same channel using the same bandwidth that is used for only a single data stream in 802.11a/b/g.

Two streams deliver twice the data. Three streams deliver three times the data. This is also why (APs) have more antennas than the older a/b/g models. At least one antenna is required per data stream, but keep in mind that not every antenna must be used for data, so the maximum number of data streams is limited by, but not necessarily equal to, the number of antennas on the AP.

This is one area where technology is just catching up with theory. The 802.11n specification allows for up to four data streams. Most currently available equipment takes advantage of only two data streams, but equipment is finally coming to market that . APs using four streams are still rare.

To take full advantage of the increased throughput the clients must also be capable of operating at the same number of data streams as the APs, and wireless client adapters are a bit further behind the APs, making three-stream capable wireless adapters still somewhat hard to come by from commercial channels.