A persistent world or persistent state world (PSW) is a virtual world which, by the definition by Richard Bartle, "continues to exist and develop internally even when there are no people interacting with it". The term is frequently used in relation to massively multiplayer online role-playing games (MMORPGs) and pervasive games.
A persistent world can be achieved by developing and maintaining a single or dynamic instance state of the game world that is shared and viewed by all players around the clock. The persistence of a world can be subdivided into "game persistence", "world persistence" and "data persistence". Data persistence ensures that any world data is not lost in the event of computer system failure. World persistence means the world continues to exist and is available to players when they want to access it. And, game persistence refers to the persistence of game events within the world (a Groundhog Day MUD is a virtual world where the entire (game) world is reset periodically). When referring a "persistent world", world and game persistence are sometimes used interchangeably. The persistence criteria is the trait that separates virtual worlds from other types of video games.
The real world is persistent. The game world of a pervasive game takes place in the real world and so pervasive games are also persistent. In other words, pervasive games shared the persistence trait with virtual worlds. An example of a pervasive game that makes heavy use of a virtual world is Can You See Me Now?, where street runners existed in a virtual world, while simultaneously running around the real physical world; the game was persistent during play, as well as the virtual world.
To give the illusion that the game world is always available, persistence can be simulated. This can be achieved by scheduling when players are allowed to play, around times when the world is offline, or as in the Animal Crossing series, having the game generate events that could have happened during the period of inactivity. Aside from virtual worlds, the simulation of a persistent world is also possible in single player games. In Noctis, players are advised to turn off the game while refueling because it takes so long. In addition, if a player who has landed on a planet stops playing and then after a while resumes, he or she can see visible changes in the sea level or the daytime/nighttime cycle. In Metal Gear Solid 3. If one stops playing long enough during the fight of Snake with "The End", he will die of old age.
A form of simulated persistence referred to as "pseudo-persistence", has been used in both in video games and pervasive games. Pseudo-persistence means making relevant world data available when the relevant players reconnect to the world instance. In a mobile game, a virtual world might exist on a distributed collection of mobile devices. If a player reconnects to a device they previously connected to, they find that their relevant world data is still present. In the video game Destiny, a World Server provides the persistent world data for the game instances (called "bubbles"), which are created on demand as a number of players are matched to play the game together.
The first game world of this kind to be introduced was the text based roleplaying game, Avalon: The Legend Lives. Prior to Avalon's inception, all forms of online roleplaying worlds featured hourly resets and reboots once players reached a certain point or once the game's puzzles were all solved. The term 'persistent world' is frequently used by players of Neverwinter Nights (2002) and Neverwinter Nights 2 (2006) to refer to MMORPG-like online environments created using the toolkits of games such as Arkaz, Avlis, Dasaria, The Known Lands and Realms of Trinity.
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