how do you
download a game
taht hasnt been released yet
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Games pre-ordered with digital download distribution software like Steam or uPlay can sometimes be downloaded prior to release, due to the large download size of the game. It also helps since less people will then download the game on launch, and since Steam has over a million users, I think trying to take the edge off the download servers at any given time is important.
Also, you have to remember, even if a game isn't released, it could be finished. Also, Steam does allow updates, so they could theoretically allow preloading and just update the game as content changes behind the scenes.