It really depends on the size of the studio. If its 3-5 guys in an apartment, they've probably got one or two servers that provide essential services -- email, source control, bug tracking, wiki, file-sharing, automated builds or other various scheduled jobs, maybe some databases. If they don't have that in-house, they've probably got at least some of that running through cloud services -- Github, VSO, Jiraa -- or perhaps runt a couple VMs and run it themselves.
Bigger studios scale this up, add some more needs, and also can't bare downtime, so you'll see them with much more serious equipment, service agreements with their vendors, and redundant systems. Also a skilled someone or someones to keep it all up and running smoothly. When you have a studio of say, 100 people who's average salary is, say 90k, and figure benfits / facilities / software/ hardware overhead at another 60k per head, a single hour's down-time costs the company $7,500 and two-and-a-half man-weeks of productivity.
So, yes, its more or less a server farm of some description, and depending on the size of the studio it might be a box or two under someone's desk, a rack in a closet, or a room full of servers and high-end networking equipment. But its the services that are most important and allow everyone to collaborate effectively.