This weekend I ran across a very interesting post on a Microsoft mailing list. It breaks down, by operating system and server/client, the unique CD keys in use for Unreal Tournament 2003 by Epic Games. (We covered the demo when it was released.) The upshot is that Linux users account for less than 1% of the keys in use as clients, with Windows accounting for almost all of the other keys. (The numbers don’t add up to 100% for clients.) On the server, 40.66% of the keys in use are on Linux machines and the remainder are on Windows. Read the actual post for the exact percentages, including a breakdown of the various Microsoft operating system releases.
While we don’t know the actual number of copies of UT2003 sold, just consider that if 1000000 (a million) copies have been sold then only 6900 of those are being used by Linux users to play the game. As usual, Linux is heavily used as a server OS.