Second Life geography spans two worlds -- the real world and the virtual world. In the real world, Second Life exists on a collection of server host machines, called sims. These computers store all the information found within the virtual world. Each sim runs between 2 to 16 server processes, which simulate regions in Second Life. Every region is 256 m2 in the virtual world. Linden Lab calls the collection of networked sims the grid.
There are many MMORPG virtual worlds out on many platforms. Most notable are IMVU for Windows, PlayStation Home for PlayStation 3, and Second Life for Windows. Many Virtual worlds have shut down since launch however. Massively multiplayer online role-playing games (MMORPGs) are a combination of role-playing video games and massively multiplayer online games in which a very large number of players interact with one another within a virtual world.
As in all RPGs, the player assumes the role of a character (often in a fantasy world or science-fiction world) and takes control over many of that character's actions. MMORPGs are distinguished from single-player or small multi-player online RPGs by the number of players able to interact together, and by the game's persistent world (usually hosted by the game's publisher), which continues to exist and evolve while the player is offline and away from the game.
Some single-player video games contain virtual worlds populated by non-player characters (NPC). Many of these allow players to save the current state of this world instance to allow stopping and restarting the virtual world at a later date. (This can be done with some multiplayer environments as well.)
The virtual worlds found in video games are often split into discrete levels.
Single-player games such as Minecraft allow players to optionally create their own world without other players, and then combine skills from the game to work together with other players and create bigger and more intricate environments. These environments can then be accessed by other players, if the server is available to other players then they may be able to modify parts of it, such as the structure of the environment.