Microsoft appears to be prepared to support third-party USB storage for saving and loading game data, according to a post by Joystiq on Thursday. The source, an alleged Microsoft engineering document, also states that the capability would be added to the Xbox 360 platform sometime this spring.

Instead of providing flash-based storage cards, the new update would allow USB hard drives to be used as storage options. There’s a catch, though: although many USB hard drives ship with capacity points higher than 16 GB, Microsoft will only allow a partition of 16 Gbytes on size, with 512 Mbytes of that used for system data. Up to two USB devices may be used, for a total of 32 Gbytes.

Here, users have two options, according to Joystiq. Let’s assume the USB hard drive is 250 Gbytes in size. Choosing a “Configure Now” option will format the drive as an Xbox partition, but transform that 250-Gbyte drive into 16 Gbytes of usable storage. But choosing the “customize” option will partition out that 16 Gbytes, leaving the remainder as storage that can not be accessed by the Xbox 360, but can be used by another machine to store music or videos.