Valve has today announced that, since its October 2007 release, Portal has sold close to four million copies – excluding Steam sales. The game first started off as a senior project titled Narbacular Drop at the DigiPen Institute of Technology in 2005, and shortly after seeing it himself, Valve boss Gabe Newell signed the development team. The finished version was then released as part of The Orange Box bundle with Half-Life 2: Episode Two and Team Fortress 2. The news emerges the day after its sequel, Portal 2, was released in North America on the Xbox 360 to great critic reviews.
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