iFixit has ripped apart Apple’s new Airport Extreme router. Instead of opting for a custom case for the new router, Apple re-uses the case with the hard drive and connectors ripped out. That means there’s a 3.5 inch drive-shaped void on the inside, just waiting to be filled with a bus-powered 2.5-inch hard drive. You could use the USB port to wire a bus powered hard drive around inside the case, as 9to5mac points out.”]
Source: https://gizmodo.com/airport-extreme-teardown-hack-this-router-with-your-ow-513080495