FM Towns computer included built-in PCM sound, in addition to a CD-ROM drive and 24-bit color graphics. By 1990, DOS was 65% of the computer-game market, with the Amiga at 10%; all other computers, including the Apple Macintosh, were below 10% and declining. Although both Apple and IBM tried to avoid customers associating their products with "game machines", the latter acknowledged that VGA, audio, and joystick options for its PS/1 computer were popular. In 1991, id Software produced an early first-person shooter, Hovertank 3D, which was the company's first in their line of highly influential games in the genre. There were also several other companies that produced early first-person shooters, such as Arsys Software's Star Cruiser, which featured fully 3D polygonal graphics in 1988, and Accolade's Day of the Viper in 1989. Id Software went on to develop Wolfenstein 3D in 1992, which helped to popularize the genre, kick-starting a genre that would become one of the highest-selling in modern times. The game was originally distributed through the shareware distribution model, allowing players to try a limited part of the game for free but requiring payment to play the rest, and represented one of the first uses of texture mapping graphics in a popular game, along with Ultima Underworld. In December 1992, Computer Gaming World reported that DOS accounted for 82% of computer-game sales in 1991, compared to Macintosh's 8% and Amiga's 5%. In response to a reader's challenge to find a DOS game that played better than the Amiga version the magazine cited Wing Commander and Civilization, and added that "The heavy MS-DOS emphasis in CGW merely reflects the realities of the market". A self-reported Computer Gaming World survey in April 1993 similarly found that 91% of readers primarily used IBM PCs and compatibles for gaming, compared to 6% for Amiga, 3% for Macintosh, and 1% for Atari ST, while a Software Publishers Association study found that 74% of personal computers were IBMs or compatible, 10% Macintosh, 7% Apple II, and 8% other. 51% of IBM or compatible had 386 or faster CPUs. By 1992, DOS games such as Links 386 Pro supported Super VGA graphics. While leading Sega and Nintendo console systems kept their CPU speed at 3–7 MHz, the 486 PC processor ran much faster, allowing it to perform many more calculations per second. The 1993 release of Doom on the PC was a breakthrough in 3D