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 first virtual worlds were text-based and often called MUDs, but the term is frequently used in relation to massively multiplayer online role-playing games (MMORPGs)  and pervasive games.  Examples of persistent worlds that exist in video games include Battle Dawn, EVE Online, and Realms of Trinity.
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.[ citation needed ] 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. 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 to a "persistent world", world and game persistence are sometimes used interchangeably. The persistence criterion 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 share 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 exist 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.[ citation needed ]
A form of simulated persistence referred to as "pseudo-persistence" has been used in both 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.[ citation needed ]. 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 toolkit. 
The first multi-player game to demonstrate on-line persistence was the text-based MUD1 written in 1978 by Rob Trubshaw and Richard Bartle. Initially only available for a few hours in off-peak time at Essex University, UK,  it featured a world reset every 105 minutes. Nevertheless, it persisted independent of players logging in for the time it was running. The subsequent decade saw many on-line worlds clone this template, but all featured variations on timed resets and reboots or did not allow players to retain objects within the game other than running point totals such as treasure or experience points as a marker of progress.
Avalon: The Legend Lives can be considered the first game to introduce a true persistent state world in 1989.  Avalon pioneered the ability for items to be retained by the player whilst offline while the Avalon realm at large continued 24/7 with only a morning backup to mark the world pausing briefly. It is currently the longest running online virtual world.
A MUD is a multiplayer real-time virtual world, usually text-based or storyboarded. MUDs combine elements of role-playing games, hack and slash, player versus player, interactive fiction, and online chat. Players can read or view descriptions of rooms, objects, other players, non-player characters, and actions performed in the virtual world. Players typically interact with each other and the world by typing commands that resemble a natural language.
A massively multiplayer online role-playing game (MMORPG) is a video game that combines aspects of a role-playing video game and a massively multiplayer online game.
AberMUD was the first popular open source MUD. It was named after the town Aberystwyth, in which it was written. The first version was written in B by Alan Cox, Richard Acott, Jim Finnis, and Leon Thrane based at University of Wales, Aberystwyth for an old Honeywell mainframe and opened in 1987.
DikuMUD is a multiplayer text-based role-playing game, which is a type of multi-user domain (MUD). It was written in 1990 and 1991 by Sebastian Hammer, Tom Madsen, Katja Nyboe, Michael Seifert, and Hans Henrik Stærfeldt at DIKU —the department of computer science at the University of Copenhagen in Copenhagen, Denmark.
Ancient Anguish, abbreviated AA, is a fantasy-themed MUD, a text-based online role-playing game. Founded in 1991 by Balz "Zor" Meierhans and Olivier "Drake" Maquelin, it opened to the public on February 2, 1992. It is free-to-play, but has been supported by player donations since 1994.
The MUD trees below depict hierarchies of derivation among MUD codebases. Solid lines between boxes indicate code relationships, while dotted lines indicate conceptual relationships. Dotted boxes indicate that the codebase is outside the family depicted.
GemStone IV is a multiplayer text-based online role-playing video game produced by Simutronics. Players control characters in a high fantasy game world named "Elanthia". The first playable version of the game was known as GemStone ][ and was launched in April 1988 on GEnie. It was one of the first MMORPGs and is one of the longest running online games still active. Access to the game is subscription-based through its website, with three additional subscriptions levels available, "Premium", "Platinum" and "Shattered", in addition to a free-to-play model introduced in early March 2015.
A massively multiplayer online game is an online video game with a large number of players on the same server. MMOs usually feature a huge, persistent open world, although there are games that differ. These games can be found for most network-capable platforms, including the personal computer, video game console, or smartphones and other mobile devices.
Player versus player (PvP) is a type of multiplayer interactive conflict within a game between human players. This is often compared to player versus environment (PvE), in which the game itself controls its players' opponents. The terms are most often used in games where both activities exist, particularly MMORPGs, MUDs, and other role-playing video games, to distinguish between gamemodes. PvP can be broadly used to describe any game, or aspect of a game, where players compete against each other. PvP is often controversial when used in role-playing games. In most cases, there are vast differences in abilities between players. PvP can even encourage experienced players to immediately attack and kill inexperienced players. PvP is often referred to as player killing in the cases of games which contain, but do not focus on, such interaction.
A virtual world is a computer-simulated environment which may be populated by many users who can create a personal avatar, and simultaneously and independently explore the virtual world, participate in its activities and communicate with others. These avatars can be textual, graphical representations, or live video avatars with auditory and touch sensations. Virtual worlds are closely related to mirror worlds.
Richard Allan Bartle FBCS FRSA is a British writer, professor and game researcher in the massively multiplayer online game industry. He co-created MUD1 in 1978, and is the author of the 2003 book Designing Virtual Worlds.
The Realm Online, originally known as The Realm, is a massively multiplayer online role playing game (MMORPG) launched in December 1996 for Windows PC. It was designed in the tradition of graphical MUDs, before the usage of the terms "massively multiplayer" and "MMORPG".
Player versus environment or player versus enemy, is a term used for both single player and online games, particularly MMORPGs, CORPGs, MUDs, other online role-playing video games and survival games to refer to fighting computer-controlled enemies—in contrast to PvP. In survival games a large part may be fighting the elements, controlling hunger and thirst, learning to adapt to the environment and exploration.
A mob, short for mobile or mobile object, is a computer-controlled non-player character (NPC) in a video game such as an MMORPG or MUD. Depending on context, every and any such character in a game may be considered to be a "mob", or usage of the term may be limited to hostile NPCs and/or NPCs vulnerable to attack.
Dragon's Gate was an interactive, real time, text-based multi user online fantasy role-playing game, sometimes referred to as a MUD. It was one of the longest running pay-for-play online games in the world, it opened to the public in the spring of 1990 on GEnie. In the summer of 1996 the game was moved to AOL. Later the game was moved to Mythic Realms, and finally to independent server, where it ran until the summer of 2007.
Achaea, Dreams of Divine Lands is a roleplay-focused, text-based multi-user dungeon (MUD) released on September 9, 1997. It was published by Achaea LLC, now known as Iron Realms Entertainment. Achaea is operated by collecting the revenue through a microtransaction system, which allows payment for the acquisition of in-game benefits.
The Bartle taxonomy of player types is a classification of video game players (gamers) based on a 1996 paper by Richard Bartle according to their preferred actions within the game. The classification originally described players of multiplayer online games, though now it also refers to players of single-player video games.
The history of massively multiplayer online games spans over thirty years and hundreds of massively multiplayer online games (MMOG) titles. The origin and influence on MMO games stems from MUDs, Dungeons & Dragons (D&D) and earlier social games.
TinyMUCK or, more broadly, a MUCK, is a type of user-extendable online text-based role-playing game, designed for role playing and social interaction. Backronyms like "Multi-User Chat/Created/Computer/Character/Carnal Kingdom" and "Multi-User Construction Kit" are sometimes cited, but are not the actual origin of the term; "muck" is simply a play on the term MUD.
Avalon: The Legend Lives is a text-based online multi-player role-playing game world that was first released on 28 October 1989 at the gaming convention Adventure 89. It has maintained a continuous on-line presence with consistent and intact persona files and player history since the late 1980s, rendering it the longest continuously running on-line role-playing game in history.
p. 23 In the teeth of complaints about wasted resources, members of the university's Computer Society were allowed to spend off-peak time doing anything non-academic they liked. Many of them chose to play MUD.