This is where the magic happens. This port is missing from the AirPort Extreme of yesteryear, which allows the Time Capsule to be a Time Capsule, and the AirPort Extreme to be... well... not so extreme.

Folks asked us if it's feasible to make an Extreme into a Time Capsule. Theoretically, the answer is "Yes," but we're not sure why you'd go through the trouble — the Seagate Barracuda drive is essentially the price difference between the Time Capsule and the Extreme.