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.
Colossal Cave Adventure
One of the first efforts to port the code was by Jim Gillogly of the RAND Corporation in 1977. Gillogly, with agreement from Crowther and Woods, spent several weeks porting the code to C to run on the more generic Unix architecture. It can be found as part of the BSD Operating Systems distributions, or as part of the "bsdgames" package under most Linux distributions, under the command name "adventure". The game was also ported to Prime Computer's super-mini running PRIMOS in the late 1970s, utilising FORTRAN IV, and to IBM mainframes running VM/CMS in late 1978, utilizing PL/I. In the late 1970s a freeware Commodore PET version was produced by Jim Butterfield; some years later this version was ported to the Commodore 64. Microsoft also released versions of "Adventure" in 1979 for the Apple II Plus and TRS-80 computers.