If you happen to own the Xbox One, I am quite sure that you already know that it would have arrived with a 500GB hard drive underneath the hood, and unlike the storage of the PS4 which can be accessed in a jiffy, the hard drive in the Xbox One was specially included so that it would be difficult for the owner to access or replace it. Still, that has not stopped some people from taking a peek around in the “forbidden territory”, where iFixit noted in their teardown that underneath the hood, you will find a 2.5” Samsung hard drive that is hooked up via a SATA II cable, so swapping it should not to be too big of a deal.
A certain Brian Williams has already attempted using a 500GB Samsung EVO SSD and a Seagate 1TB hybrid SSHD as replacements, only to figure out that the boot time had a slight improvement. For instance, a test involving Call of Duty: Ghosts saw the SSD take 27 seconds to load the game, while the hybrid drive was a wee bit behind at 27.7 seconds, shaving off 6 seconds or so from the 33.5 seconds for a stock model. Since the performance gains are not that significant at all, it would be better to leave your Xbox One alone.