As Xbox 360 owners know by now, GTA 5 is coming on two discs, just Forza 4 did. The first disc is the “install” disc, which is installed to the hard drive. The second disc is he “play” disc and as you can guess this disc needs to be in the drive to play the game. The installation of the install disc takes about 7.7GB of hard drive space, which is a requirement that is spelled out on the box.
Rumors have suggested that if you have a fast and large USB drive, you could apparently install the “play” disc on the USB stick and that seems to nullify the issue of encountering problems by installing the “play” disc to the hard drive. Of course we have only heard whispers of this working and we have not tested this formula out for ourselves.