A massively multiplayer online (MMO) game server is a computer that acts as a host for people who are playing the game. The MMO server runs a host version of the game software, while players run client versions on their computers. Players are sometimes able to connect to an MMO server though a server browser, though in many cases their characters are locked into one server or another. Most MMOs have multiple servers to help distribute the load across a number of different computers and physical locations; players are typically only able to interact with people who are connected to the same server. Single server architecture also exists, though it is not as common.
Massively multiplayer online games are computer and video games that allow a great number of people to all play together in a persistent world. A lot of MMOs are role playing games (RPGs), though many other genres are represented as well. The most important component in the infrastructure that allows these games to exist is the MMO server. Different games use a variety of server infrastructures, though they typically operate on a basic host and client model. Unlike conventional video games that rely on a player to act as host, MMOs always use a server as the host and require the players to connect as clients.
Due to the fact that most MMO games use persistent worlds, it is typically necessary for an MMO server to stay up and connected to the Internet at all times. The server continues to simulate events, and keep track of player accomplishments, even after people have signed off. When it becomes necessary to perform maintenance on an MMO server, everyone is typically forced to log off so that the computer or server files can be worked on.
Many MMO games use a multiple server architecture, where identical copies of the game world exist on a number of different servers. Some of these games allow players to move between servers at will, while others lock players or their characters into a specific server for load balancing purposes. Servers are sometimes hosted on dedicated computers, though multiple game servers can also exist on one host. Some MMOs use a single server architecture, which allows all of the players to connect to the same virtual world. These games are often designed so that players in certain parts of the game world have very little interaction with players outside of that area.
Private game servers essentially consist the host software of an MMO running on hardware that is not owned or operated by the designer or publisher of the game. This usually is not allowed according to software end user license agreements (EULAs), though there are some exceptions. Some older MMOs that are no longer operated have had the code released openly so that players can run their own private servers. These private servers are typically very resource intensive, and usually need to be run on dedicated computers that have robust Internet connections.