What types of servers or equipment does online gaming use?

[Lethn]

As someone who's been wanting to make games for years, now I'm learning programming I've started getting curious about networks and particularly the big MMORPGs, I'm glancing around occasionally but I was wondering if anyone here knew exactly what sort of hardware MMORPG companies in particular hosted their games on? Would it be something like a Virtual Private Server? Or do you need something far more specialised depending on the game, I'm thinking in terms of something like Planetside 2 with the scale.