Halon used to be the standard for data centers using gaseous fire extinguishers in the mainframe era. See: http://www.catb.org/jargon/html/D/dinosaur-pen.html

The op's a bit outdated, but not completely wrong. Even now a lot of data centers use various halon replacements rather than Argonite, though there are a number of different gaseous fire suppressants used in data centers these days.