on mainframes and minicomputers had previously already existed. OXO, an adaptation of tic-tac-toe for the EDSAC, debuted in 1952. Another pioneer computer game was developed in 1961, when MIT students Martin Graetz and Alan Kotok, with MIT student Steve Russell, developed Spacewar! on a PDP-1 mainframe computer used for statistical calculations. The first generation of computer games were often text-based adventures or interactive fiction, in which the player communicated with the computer by entering commands through a keyboard. 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. Later games combined textual commands with basic graphics, as seen in the SSI Gold Box games such as Pool of Radiance, or The Bard's Tale, for example. Early personal computer games By the late 1970s to early 1980s, games were developed and distributed through hobbyist groups and gaming magazines, such as Creative Computing and later Computer Gaming World. These publications provided game code that could be typed into a computer and played, encouraging readers to submit their own software to competitions. Players could modify the BASIC source code of even commercial games. Microchess was one of the first games for microcomputers which was sold to the public. First sold in 1977, Microchess eventually sold over 50,000 copies on cassette tape. As with second-generation video game consoles at the time, early home computer game companies capitalized on successful arcade games at the time with ports or clones of popular arcade video games. By 1982, the top-selling games for the Atari 400 and 800 were ports of Frogger and Centipede, while the top-selling game for the TI-99/4A was the Space Invaders clone TI Invaders. That same year, Pac-Man was ported to the Atari 8-bit computers, while Donkey Kong was licensed for the Coleco Adam. In late 1981, Atari, Inc. attempted to take legal action against unauthorized Pac-Man clones, despite some of these predating Atari's exclusive rights to the home versions of Namco's game. Industry crash and aftermath As the video game market became flooded with poor-quality cartridge games created by numerous companies attempting to enter the market, and overproduction of high-profile releases such as the Atari 2600 adaptations of Pac-Man and E.T. grossly underperformed,