Major Nelson has confirmed in his PAX Podcast that the Xbox One will not support external storage at launch. The system has 500 GB internal drive, and they’ve said that you can’t alter the internal either. The Xbox One will ship with a 500GB hard drive, all of them have that. The future plan is definitely to support external storage, much like we do on the Xbox 360. My understanding is that feature won’t be there at launch because the team’s working on other things. It’s definitely on the list, but I don’t know when it’ll come in though. Source - NextVG
For some reason this annoys me! I dont understand why such a small feature cant be included on day one!