Generally, all the worlds are the most heavily populated and therefore impossible to enter for Free2Play players. This has became a lot bigger problem with the removal of 3rd server.(Usko is "Game is free to play, but it's not free to login"). Generally the Pathos and Logos servers are a bit less populated than the others. Nearly all of the people who play Knight Online are Turkish, which is why the game is crowded around their afternoon/evening. Players are allowed to have up to three characters on each server, but all of the players on the server must be from the same race. To have one character that is human and one character that is orc, a user would have to make one of them on a different server. Each world is further divided into two sub-servers (ex. Ares1, Ares2). Players can use a character from a certain world on any of that world's servers, however it is not possible to transfer characters/items/money between worlds. Some zones/events including War, Delos, the Abyss, and Ardream can only be accessed from server one in each world, which typically has the most users logged in at any given time.
However, the recent implementation of the new Carnac-West server allowed players from North America, parts of Europe, Australia, and a few other countries to have an isolated access to this server. By preventing players with IPs from other countries, the server population of Carnac-West was greatly reduced, drastically eliminating the login issues for players of the permitted geologic regions.