Unfortunately, the Xbox One doesn't officially feature a replaceable hard drive—but then, we're not much for playing by the rules. Out it comes.
Bad news: replacing the hard drive requires voiding the warranty. Good news: it's a standard 2.5 inch SATA II drive. Sad news, the Xbox One doesn't support unformatted hard drives.
Inside our Xbox One, we find a Samsung Spinpoint M8 ST500LM012 500 GB 5400 RPM with 8MB Cache SATA II 3.0Gb/s hard drive.