The Xbox is a games console produced by Microsoft starting on November 15, 2001. It directly rivals Sony's PlayStation 2. The successor to the Xbox is Microsoft's Xbox 360, which features major improvements from the original Xbox and it also rivals Sony's PlayStation 2 successor, PlayStation 3 and other current generation consoles. Due to the Xbox 360's success, Xbox stopped being manufactured by Microsoft in late 2006.
Due to Rockstar Games producing Grand Theft Auto games for PlayStation first, all ports to the Xbox came a few years after the original release of the any GTA game.
This changed after the release of the Xbox 360, as the Xbox 360 and PlayStation 3 versions of the game came out on the same date.