An early text-adventure, Adventure, was developed for the PDP-11 minicomputer by Will Crowther in 1976, and expanded by Don Woods in 1977. By the 1980s, personal computers had become powerful enough to run games like Adventure, but by this time, graphics were beginning to become an important factor in games. By 1988, the enormous popularity of the Nintendo Entertainment System had greatly affected the computer-game industry. By 1987 the PC market was growing so quickly that the formerly business-only computer had become the largest and most important platform for computer game companies. IBM and others sold some games like Microsoft Flight Simulator but the PC's CGA graphics and speaker sound were poor, and most customers bought the expensive but powerful computer for business. From mid-1985, however, what Compute! described as a "wave" of inexpensive IBM PC clones from American and Asian companies caused prices to decline; by the end of 1986, the equivalent to a $1600 real IBM PC with 256K RAM and two disk drives cost as little as $600, lower than the price of the Apple IIc. While many companies used the additional storage to release poor-quality shovelware collections of older software, or "enhanced" versions of existing ones, new games such as Myst included many more assets for a richer game experience. Although both Apple and IBM tried to avoid customers associating their products with "game machine"s, 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.