This is from an article on Dark Age of Camelot from 2003:
The heart of Camelot, it turns out, isn't in the English countryside but in Fairfax, Virginia. There Mythic keeps 120 dual-processor Pentium servers running linux. Each group of six servers runs what mythic calls a gamespace—a virtual world inhabited by thousands of players. The idea is to create different gamespaces for different types of players.
Design decisions also reflect the need to keep players happy. While each gamespace could conceivably handle 20,000 simultaneous players, Mythic limits them to about 4,000 players each, adding new gamespaces when necessary instead of increasing the load on the ones already up. "If you have too many people, the worlds get too crowded," says Denton. "The last thing you want is to be bumping into thousands of people."
We also have multiple example of CIG trying to market common tech (serialized variable!) as some of milestone.