Apple released simultaneous 2.4/5 GHz base station upgrades today to its two full-featured products: Apple's AirPort Extreme is in its sixth revision with the same name, by my count, and its third featuring 802.11n. The latest release moves from either 2.4 or 5 GHz 802.11n networking to supporting both bands at the same time. This is a hardware update, requiring a new unit, as Apple added a radio to the mix.
Apple also updated its Time Capsule model, an Extreme base station that comes with an internal 500 GB or 1 TB hard drive for backups and networked file sharing. Prices are the same as the previous one-band-at-a-time models: $179 for Extreme; $299 for a 500 GB Time Capsule; and a ludicrous $499 for a 1 TB Time Capsule.
Both units have four gigabit Ethernet ports, configured as 1 WAN and 3 switched LAN ports or as a 4-port switched LAN in bridged mode. Both models have a USB port that allows a printer or hard drive to be attached, or, using a USB hub, multiple devices of each kind.
Apple ships configuration software for both Mac OS X and Windows, and the system is fully compatible with Windows.
The company told me it incorporated small changes to its Mac OS X adapter hardware that allows a Mac to select the faster network if both 2.4 and 5 GHz networks are named identically. This change doesn't break Wi-Fi interoperability, but goes beyond the process that adapters use to select among available networks today. The 2.4 and 5 GHz networks may be named uniquely.
New features were added as well. Guest networking is a neat addition, using a virtual SSID and virtual LAN to create a network for guests that's got a separate encryption key and cannot see the traffic of the main network nor its Ethernet portion.
Apple also added remote secure file-sharing access to any internal or external drive on either base station model using its Back to My Mac service, which debuted in Leopard. The service requires MobileMe, a $100/year email and file-storage subscription service. Mac OS X 10.5 Leopard can initiate a strongly encrypted tunneled connection with any other Leopard system or, now, new base station that's configured with the same MobileMe account.
Those interested in deeper detail should consult my Macworld article.