The Guild Wars Servers host and coordinate the games. All data are saved here. Players must connect to a server to be able to play. There is no offline playing, not even basic training or tutorials.
While the server is commonly referred to in singular form, it is actually a large cluster of numerous individual server boxes connected and working together. ArenaNet refers to these server clusters as "data center". As Jeff Strain explains in this interview, a data center consists of approxminately 12 different types of servers, with each type specialized in a different task (authentication, guild management, gaming, tournament, chat, etc.). The number of servers of each type is adapted dynamically to the workload (depending on number of active instances / districts) to ensure lag-free performance.
Worldwide, there is currently one data center per territory. These data centers are again connected to a worldwide network, unlike most other MMORPGs that have independent servers ("shards"). This allows players from all over the world to play together and to compete against each other in the Global Tournament. The key to provide lag-free gaming worldwide is ArenaNet's intelligent server management. The a.m. data centers are all linked and optimize connections automatically / dynamically as players join a party. ArenaNet's Jeff Strain explains a bit about this in this interview:
- "Our server infrastructure is actually kind of reflective of our core technology. We have data centres all over the world - we have data centres in Europe, data centres in the US, Korea, Japan and Taiwan. As you know, when you create your account in Guild Wars, it's a global account - you don't pick one of those data centres or servers, you're not even really aware of them.
- What happens is that it knows where you are, and when you play, you'll probably be connected to one of the European servers - if you're playing with your buddies, or by yourself, in general it knows your home datacentre. But if you want to play with me, and I'm on one of the US datacentres, the datacentres will communicate with each other and try to figure out the best place to host our game. They may decide that the total experience across both of us is going to be better if it hosts the game in Europe, and so it'll hand off my character - it migrates my character record temporarily to the European datacentre, you and I play our game, and then when we're done, it migrates my character back.
- The datacentres all work in a confederated manner. It's presented to you as one big massive server that's serving the entire world, because you never have to be aware of where they are, but there's a lot of datacentre communication going on on your behalf in the background to make sure that it's optimising the play experience for you.
- As a specific example of that, we just had a world championship event in Taiwan, where we had six Guilds - two from Europe, two from the US, and two from Korea. When they played, they were all playing on servers in Taiwan, because it knew where they were playing and it migrated their server records to Taiwan for that match - so that the latency was optimal."