Open world
There is no consensus on what the earliest open world game is, due to differing definitions of how large or open a world needs to be. Ars Technica traces the concept back to the free-roaming exploration of 1976 text adventure game "Colossal Cave Adventure", which inspired the free-roaming exploration of "Adventure" (1980), but notes that it wasn't until 1984 that what "we now know as open-world gaming" took on a "definite shape" with 1984 space simulator "Elite", considered a pioneer of the open world; Gamasutra argues that its open-ended sandbox style is rooted in flight simulators, such as SubLOGIC's "Flight Simulator" (1979/1980), noting most flight sims "offer a 'free flight' mode that allows players to simply pilot the aircraft and explore the virtual world". Others trace the concept back to 1981 CRPG "", which had a free-roaming overworld map inspired by tabletop RPG "Dungeons & Dragons". The overworld maps of the first five "Ultima" games, released up to 1988, lacked a single, unified scale, with towns and other places represented as icons; this style was adopted by the first three "Dragon Quest" games, released from 1986 to 1988 in Japan.
Microsoft Adventure
"Microsoft Adventure" is an implementation for personal computers of the PDP-10 mainframe game "Colossal Cave Adventure". Microsoft originally released "Microsoft Adventure" in 1979 for the TRS-80 and the Apple II under its new division, Microsoft Consumer Products. It was written for the company by Gordon Letwin of Softwin Associates, and was available for the list price of US$30. IBM later included "Microsoft Adventure" as the only game in the initial software release for its IBM Personal Computer. It was released in 1981 for the initial version of IBM PC DOS (1.0) as a launch title, making it the first commercial game available for the new computer. It was released on a single-sided 5 inch disk, required 32K RAM, and booted directly from the disk; it could not be opened from DOS. Microsoft's "Adventure" contained 130 rooms, 15 treasures, 40 useful objects and 12 problems to be solved. The progress of two games could be saved on a diskette.