It sold an estimated 3.5 million copies by 1999 among ten and 20 million individuals are believed to have performed it inside of two a long time of start, and in late 1995, it was estimated to be mounted on extra personal computers globally than Microsoft's new working program, Windows ninety five. Along with Wolfenstein 3D, Doom assisted define the FPS style and motivated several identical games, usually called Doom clones.