With the Xbox 360, you have the ability to replace the hard drive with any laptop computer sized 2.5 inch SATA hard drive. You can upgrade your storage space cheaper this way than buying Microsoft packaged hard drives. When you install a new hard drive into your Xbox 360, you must format it for it to be recognised by your Xbox as a storage device.
Turn on your Xbox and navigate to the “System Settings” option on the “My Xbox” blade of the Xbox 360 dashboard.
Select “Memory” from the list of options.
Highlight the storage device you wish to format, which will be labelled “Hard Drive,” and press the “Y” button on the Xbox controller.
Select “Format” and confirm that you wish to delete all of the drive's contents in order to format it for the Xbox 360.
Enter your console's serial number if you are prompted to do so. The serial number is located on the bar code on the back of the console and inside of the USB port on the front of the console. After entering the number, select "Done." Your hard drive will now be formatted, and you will able to store Xbox data on it once it finishes.