A cnet post quotes the NYSE:

The New York Stock Exchange is investing heavily in x86-based Linux systems and blade servers as it builds out the NYSE Hybrid Market trading system that it launched last year. Flexibility and lower cost are among the goals. But one of the things that NYSE Euronext CIO Steve Rubinow says he most wants from the new computing architecture is technology independence.

“What we want is to be able to take advantage of technology advances when they happen,” Rubinow said. “We’re trying to be as independent of any technologies as we can be.”

Source: Linux gives the NYSE lower costs and independence by Matt Asay – CNET Blogs