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The first Halo game, Halo: Combat Evolved or Halo: CE is about 600MB.
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There are currently seven (7) Halo Series Video Games: Halo: Combat Evolved, Halo 2, Halo 3, Halo Wars, Halo 3: ODST, Halo: Reach, and Halo: Combat Evolved 10th Anniversary Edition. The release of Halo 4 from 343 Industries will increase the total to eight (8).
Currently 5 with an upcoming 6th in late 2010 Halo: Combat Evolved Halo 2 Halo 3 Halo Wars Halo 3 ODST Halo Reach
In the first game's campaign, Halo: Combat Evolved, there are 10 levels. These include: "The Pillar of Autumn', "Halo", "Truth and Reconciliation", "The Silent Cartographer", "Assault on the Control Room", "343 Guilty Spark", "The Library", "Two Betrayals", "Keyes", and "The Maw".For a complete list of all levels, multiplayer and campaign, of all the halo games, visit:http://halo.wikia.com/wiki/List_of_Halo_Levels
As of the time of typing the Halo series has had the following games Halo: Combat Evolved Halo 2 Halo 3 Halo Wars Halo 3 ODST Halo Reach Halo 4
Up to two players can play in the Co-Op Campaign mode on Halo: Combat Evolved.
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Many Halo's have been released for the Xbox. (list of Halo games, in order of release date) Original Xbox: Halo Combat Evolved (November 15, 2001) Halo 2 (November 09, 2004) Xbox360: Halo 3 (September 25, 2007) Halo Wars (March 03, 2009) Halo 3 ODST (September 22, 2009) Halo Reach (September 14, 2010) Halo Combat Evolved Anniversary Edition (November 15, 2011) Halo 4 (Coming Soon)
Well, as of now, there are currently three main Halo Games. Halo Combat Evolved. Halo 2. Halo 3. There are three spin-offs. Halo Wars. Halo 3: ODST Halo Reach And of course, you've got Halo 4 due for a release soon.