Xbox 360 Units
As of 2010, the latest Xbox 360 consoles have an internal hard drive of either 4 GB or 250 GB depending on the model. These models come fully capable of performing all the duties featured by the older Xbox 360 models.
Xbox 360 External Hard Drives
Prior to the 2010 Xbox 360 models, older units required an external Xbox 360-brand hard drive if the user wanted to download content from the Xbox Live Marketplace, or rip music to the console. These hard drives vary in size from 20 GB to 250 GB and are compatible with all older Xbox 360 consoles.
Third-Party USB Hard Drives
As of April 6, 2010, a system update allows Xbox 360 consoles to use 16 GB of memory from third-party USB hard drives after a simple configuration process.