The largest officially supported internal hard drive for the Xbox 360 (S and E models) is 250 GB (Microsoft part numbers: X814740-001, X814740-002).
External Drives
USB flash drives / external HDDs up to 2 TB are supported for game storage (formatted as Xbox 360 storage device).
But: The console's dashboard only recognizes up to 250 GB per device (later dashboard updates raised this to 2 TB for USB, but many users report 250 GB practical limit on older dashboards).
You can use multiple USB drives (up to 2 simultaneously).
What About 320 GB / 500 GB Drives?
Some 320 GB drives were bundled with limited-edition consoles (e.g., Modern Warfare 2 250 GB + 120 GB? No—250 GB was max retail).
500 GB laptop drives (2.5" SATA) work physically but the 360 firmware caps usable space at 250 GB. The rest is invisible.
Practical Advice
For digital games + DLC: 250 GB internal + 1–2 TB USB = ample.
For disc-based games: 120–250 GB internal is fine (installs optional).
Always use official Microsoft drives or known-compatible Western Digital Scorpio (WD2500BEVT) for internal to avoid "unauthorized storage" errors.
