Time Capsule is rather cool. The new hardware device from Apple, introduced at Macworld Expo last week in San Francisco, combines a complete AirPort Extreme Base Station with gigabit Ethernet (the model released late in the second quarter of 2007) and an internal hard drive at a reasonable price for the combination. That AirPort Extreme Base Station by itself costs $179, making the $299 price for 500 GB and $499 price for 1 TB a decent deal. (See "Time Capsule Bundles AirPort Base Station and Backup Disk," 2008-01-15.)

The Time Capsule is designed to act as a Time Machine backup drive for a network, offering a capability that otherwise requires a networked Mac running file sharing in Mac OS X 10.5 Leopard to act as the backup destination. The Time Capsule drive can also be mounted like a network-attached storage (NAS) server.

(Before you ask: Time Capsule really is just a hard drive in a case combined with the current AirPort Extreme base station hardware. There are no extra features, unless you count the absence of a power brick. Unlike the regular AirPort Extreme, Time Capsule has an internal AC-to-DC converter and needs only a supplied power cord.)

But this simple device has produced a lot of anger. All week I heard people asking the question and then getting somewhat mad at the answer: "Can I now plug a regular drive into an older AirPort Extreme via USB and use that with Time Machine?" No, dear readers, no.

I've now heard from many people with connections to Apple engineers that the Time Machine support for NAS volumes on the AirPort Extreme was pulled from Leopard before the operating system shipped because of reliability issues. (Roughly Drafted published email from a reader explaining this back in November 2007; Joe Kissell discussed overall Time Machine problems, including this one, in "Time Machine: The Good, the Bad, and the Missing Features," 2007-10-28.)

But if Apple can now reliably write backups to a hard drive connected via Serial ATA, why can't it handle a drive connected via USB? And what does it say about the NAS support if backups can't be reliably written?

It's a mystery, but I have a sneaking suspicion that the answer will be a firmware upgrade for the current AirPort Extreme Base Station that accompanies the actual release of the Time Capsule next month. Hopefully that upgrade will be free, because many people bought an AirPort Extreme for the express purpose of using Time Machine with it.