Essentially, the whole architecture of the basis of how the mod worked has changed as well, previously the way DayZ worked was your client was connected to the server and that server connected to a database, that’s problematic for security and a bunch of other reasons and it was very difficult for the mod to realise when a player had left the game. Now Dean has complete control so when the application knows it’s closing it can force saves and things like that, now is you have the client, you have the game server, the game server talks to a central server and then that central server talks to the database.
So it’s really easy to control stuff like combat logging now as you don’t control when you disconnect, the server controls everything, you don’t log out until the server logs out out and if you just disconnect your player is just going to be hanging around until the server decides to clean it up.
This is why we don’t know when we are going to be released because we have taken a game that operates in one way and changed it into an MMO (done by our lead programmer who was the guy who wrote Operation Flashpoint and set up BIS).
In terms of netcode, the way ArmA II works is all of the clients calculate their own simulation for objects so lets say I fire my gun, all clients are notified that I fired my gun and they compare notes on the server and it’s usually the client who that object was local to that decides the outcome but there is no real umpire, everyone figures it out on their own and then tries to resolve it, in the standalone, the server decides. So that’s why it’s taking time and in the meantime the development team is looking at zombies, pathfinding, how they attack etc (source).