Xbox
From Halopedia, the Halo wiki
The Microsoft X-Box is the electronic console which both Halo: Combat Evolved and Halo 2 are played on. It was developed by the Microsoft Corporation.
Through the X-Box, a player can connect to X-Box live, play with three other players on a single console, and play with 36 players (total) online.
Both games were originally designed to be played on the X-Box, making the PC versions consierably poorer in visual, audio and multiplayer quality.