The Xbox 360 Premium model included a 20 GB hard drive at launch.
Microsoft released the Xbox 360 in November 2005 with different configurations. The Premium package was the higher-end launch version and included a detachable 20 GB hard disk drive, while the less expensive Core model launched without a hard drive. The hard drive stored game saves, downloadable content, Xbox Live Arcade titles, music, and other user data.
The 20 GB figure describes the drive’s advertised capacity, not the amount available for personal files. System software and reserved space reduced usable storage. Microsoft later introduced larger Xbox 360 hard drives, including 60 GB, 120 GB, and 250 GB models, as digital downloads and installed games became more common.
This detail is often confused with the Xbox 360’s later storage upgrades or with the console’s external USB storage support. The original Premium launch specification was specifically a 20 GB internal detachable hard drive.