According to the recent mini teardown of the 2013 Airport Time Capsule, the device holds a standard 2 TB Seagate drive. http://www.ifixit.com/Teardown/AirPort+Time+Capsule+A1470+Teardown/15067/1 The question is whether you can make a DYI upgrade to a 4 TB drive. Previous Time Capsules had an issue with the drive size when swapping the drive to a 4 TB as it wouldn't properly recognize the drive and capacity. I also recall that recent iMacs had a harddrive with a modified firmware. Wonder whether the TC drives are actually not-so-standard and have a modded firmware as well. Would be interesting to see how things play out with this new APTC.