AirPort Express and AirPort Extreme support simultaneous dual-band 802.11n Wi-Fi. That means they transmit at both the 2.4GHz and 5GHz frequencies at the same time. So no matter which band your Wi-Fi devices use, they’ll automatically connect to the best available band for the fastest possible performance. AirPort Express and AirPort Extreme are compatible with devices using the 802.11a, 802.11b, 802.11g, and 802.11n specifications and have a built-in firewall.
With AirPort Express, you can also take advantage of included AirPlay technology to wirelessly play your iTunes music library on speakers connected to the Airport Express. Airport Express also includes a 10/100 BASE-T Ethernet port.
With AirPort Extreme, you can even turn an external USB hard drive into one that can be securely shared with other users on your network, or remotely over the Internet. Airport Extreme also includes three Gigabit Ethernet ports.