Planet MarZ

One common characteristic of MMOGs is that they allow you to play along with large numbers of other people in the same game environment. Not only does playing involve some sort of combat, it can also include things like trading and negotiating. Even if a game caps the number of players that can engage in a single battle, there is rarely a limit on how many players can partake in economic aspects of the game. A game like Battlefield 2, which offers a persistent stats system even though matches have relatively small player limits, might be considered a MMOG. Similarly, if thousands of people are competing for a high score in a game of Pac-man, that doesn't make Pac-man a massively multiplayer game.

Another thing to consider is that, text-based games excluded, there are limits to how many players can play at the same time. Graphical games split their user-base across a number of different servers, also referred to as "shards" or "realms," each of which is a complete version of the game but split into different worlds and different players. The population limits of servers vary from game to game, but they frequently support several thousand players each.

World of Warcraft is one game where everyone on a realm could all decide to congregate in a single zone, and there have been in-game events, such as the opening of the Gates of Ahn'Qiraj, that brought very large numbers of players into one place. Situations like this increases lag inevitably, information gets lost, characters near your own stop getting rendered, and the server begins to drop connections or crashes altogether. The problem is that each additional character in the area increases the amount of data that must be sent to everyone exponentially which may overwhelm the system.

While many games have demonstrated that it is possible to have hundreds of active players in a single area, they try to spread players out in order to minimize lag.