802.11ac supplements 802.11n
802.11ac (aka 5G Wi-Fi) is the next step after 802.11n (aka N or Wireless-N, which is currently is the most popular Wi-Fi standard). It’s backward-compatible with N, meaning that a 5G Wi-Fi router will support N clients and 5G Wi-Fi clients will also be able to connect to an N router. Wireless-N, in turn, is backward compatible with the rest of the wireless standards, including 802.11g, 802.11b, and 802.11a.
How 802.11ac is different from 802.11n
The biggest difference, other than the improved speeds, that 802.11ac has over Wireless-N is the fact that 5G Wi-Fi works solely on the 5Ghz band and supports channel width, for now, up to 80Mhz (as opposed to 20Mhz of N).
To make 802.11ac hardware truly backward-compatible with N devices, which are available in both 2.4Ghz and 5Ghz bands, all 5G Wi-Fi devices will come with 802.11n on the 2.4Ghz band.
What is 802.11ac good for?
Everything. I can’t imagine how the faster connection speed would hurt you. However, the new standard is especially good for high-def streaming within a local network. In arecent demo, Netgear showed that it could instantly play back four different 1080p movies wirelessly to four HDTVs using 802.11ac connections, something not possible with Wireless-N.
802.11ac clients are also supposed to offer much better battery life than N clients. This is mostly thanks to the improved speed. The fact that 5G Wi-Fi clients can finish transmitting the same amount of data in just around 1 third of the time, compared to N clients, translates into less energy being used.