 Apple describes it as a "Backup Appliance", designed to work in tandem with the Time Machine backup software utility introduced in Mac OS X 10.5.Introduced on January 15, 2008 and released on February 29, 2008, the device has been upgraded several times, matching upgrades in the Extreme series routers.The earliest versions supported 802.11n wireless and came with a 500 GB hard drive in the base model, while the latest model, introduced in 2013, features 802.11ac and a 3 TB hard drive.