"You'Re About To Go into the Death Star," Joffe says. A balding, goateed guy with narrow, rectangular glasses, Joffe places his palm in a biometric scanner in the first-floor lobby of a building near Sony Online Entertainment's main offices, and a gray door unlocks noiselessly.

The Death Star is a huge, warm, windowless room containing the rows and rows of servers that run Sony's online games. The whooshing of a massive air-conditioning system is so loud that conversation is almost impossible. A large steel cage surrounds more than 500 servers stacked 32 high in towering racks—and this is just one battalion, albeit the largest, in Sony's 1500-machine army of servers.

Other than the graphics and sound, which are loaded directly onto the players' machines from CD-ROMs when EverQuest is installed, everything else needed to run the game—including the players' characters—is stored on these machines. Sony calls them "world servers."

It's more than just a catchy name. Remember that to prevent overcrowding, EverQuest is divided into dozens of parallel worlds. The worlds are reflected in the server farm as interconnected combinations, or clusters, of servers; the cluster size is based on how many users Sony expects to support simultaneously. In other words, each world is a cluster consisting of between 20 and 30 dual-processor computers. And within the clusters, individual processors are devoted to producing different pieces of geography—a town, a forest, a labyrinthine castle—in those worlds.

When a player logs on to the game, the program, or client, being used connects to servers in the cluster the character was last playing in. Those servers then download data describing everything—the alter egos, locations, weapons, and other characteristics of other players who are logged on, plus all the relevant monsters and weapons nearby. A full EverQuest install, which requires six CD-ROMs, weighs in at about 3 gigabytes. To log on, players must have the latest version of the software, which is updated through downloadable patches every two to four weeks.

When the patch is large—say, 25 or 30 megabytes—play stops and Sony takes the servers down for as long as several hours (but usually less than 30 minutes). During that time, Sony updates the code on the servers and sends the new software to the players. The patches are not merely fixes to problems. They can be brand-new content—a new city, dungeon, or continent to explore.

Each world can support about 2500 players at a time, although it can store data on up to 10 000. When EverQuest launched in 1999, there were just 12 worlds supporting 100 000 players. Last year there were 52 supporting half a million.

As the game's audience expands and evolves, so does the architecture behind the scenes. The process begins every time Sony adds big new chunks of content to an existing world. New dual-processor servers are first added to the rack deep inside the Death Star. The more content required, the more machines are pressed into service to provide it.

Once Joffe's team adds a server to the rack, he loads a Unix operating system onto it. Custom-built software then automatically loads all the game software and the programs the new machine uses to communicate with other servers, configures its storage systems, and starts it up. The server is then ready to be added to the cluster that supplies data about a particular world in EverQuest. The entire process of joining the server farm occurs within minutes, Joffe says. As characters populate the virtual locales that the new machine produces, their data are stored there.

All those expansions make for a crowded server room. To be able to keep expanding its computing power without outgrowing the Death Star, Sony has begun using blade servers. Stacked like books on a shelf, the slim computers share certain hardware—such as power supplies, cooling fans, and network interfaces—among themselves, allowing more servers to be housed in a single rack [see "Blades Have the Edge," IEEE Spectrum, April 2005]. But even blades have their limitations. "Blades are so dense that they produce too much heat," Joffe says. "You can stuff them into small spaces, but you need space to cool them properly."