large to fit into a 5¼-inch floppy disk, so he devised a way to convert the images into coordinates and instructions for the program to redraw the lines of the scenes rather than static images, as well as writing a better version of the VersaWriter scanning software. The resulting game is a text-based adventure with a depiction of the character's location displayed above the text. The game's code was completed in only a few days, and was finished on May 5, 1980. The couple took out an advertisement in Micro magazine as On-Line Systems, and mass-produced Ziploc bags containing a floppy disk and a sheet of instructions, to be sold at . Reception and legacy To the Williams's surprise, what Roberta had initially considered a hobby project sold more than 10,000 copies through mail-order. Including its 1982 rerelease through the SierraVenture line, 80,000 units were eventually sold worldwide, making it one of the best-selling computer games at the time. Mark Marlow reviewed Mission: Asteroid, Mystery House, and The Wizard and the Princess for Computer Gaming World, and stated that "Mystery House is considerably more difficult and provides many traps for the unwary in a wonderfully Victorian setting." Computer Gaming World in 1996 ranked it fourth on the magazine's list of the most innovative computer games. GamePro named Mystery House the 51st most important game of all time in 2007, for introducing a visual component to adventure games and for featuring graphics at a time when most computer games did not. Though the game is often considered the first adventure game to use graphics, dungeon crawl role-playing video games had already been using graphics prior to its release. Applying graphics to an adventure game, however, was unprecedented as previous story-based adventure games were entirely text-based. Mystery Houses success led the Williams to create the Hi-Res Adventures series, and note the game as Hi-Res Adventure #1. After the follow-on success of their next game, Wizard and the Princess, the pair moved into game development full-time, and On-Line Systems was incorporated in 1980 as Sierra On-Line. The game was later released into the public domain in 1987 as part of Sierra's seventh anniversary celebration. In Japan, several different adventure games under the title Mystery House were released. In 1982, MicroCabin released Mystery House, which was unrelated to (but inspired by) the On-Line Systems game of the same name. The following year, the Japanese