802.11n vs 802.11ac
The iMac (21.5-inch, Mid 2011) only supports-802.11 a/b/g/n. This is useful to know since many newer WiFi Routers are now supporting 802.11ac and there's a big difference between the-802.11n and-802.11ac. The latest routers from Comcast, as part of xFinity X1 upgrades now support 802.11ac speeds.
- 802.11n - Was approved in 2009 and can handle speeds of at least 600 Mbit/s
- 802.11ac - Was approved in January 2014 and can handled speeds of at lease 1 gigabit her second.
User's of older iMac's can take advantage of the higher speed by getting an adapter.
Your best bet is the-NETGEAR WiFi USB 2.0 Adapter - AC Dual Band (A6200), which sells for about $24.99 on Amazon.-
Mono price has a-Dual-Band 802.11AC 600Mbps USB 2.0 Wi-Fi- Adapter for $12, but your just getting-speed of up to 433Mbps. So you are basically getting the 802.11n speeds.