The New York Stock Exchange and its European subsidiary exchanges are running their trading systems on Red Hat (NYSE: RHT) Enterprise Linux, Red Hat announced Wednesday, as it unveiled a new marquee customer.

Linux has been known to be in use at several New York financial services firms, but few have stepped up to the podium to testify on the value of their implementations. As a result of mergers and acquisitions, the New York Stock Exchange has migrated over the last few years fromHP (NYSE: HPQ)-UX to IBM (NYSE: IBM) AIX to Sun Solaris to Linux. NYSE Group CIO Steve Rubinow said the conversion to Linux followed the acquisition of the Euronext exchange in 2007. Unlike some trading companies that suggest Linux is running their secondary systems, Rubinow emphasized that Linux is running the NYSE's mission-critical trading systems.

"Red Hat is like water; it's pervasive within our architecture. ... Without it, most of our computers wouldn't be running," he said in a prepared statement and in a video recorded for Red Hat's Web site.

Instead of running on proprietary hardware, the exchange, now known as NYSE Euronext, runs on 200 four-way HP ProLiant DL585 servers and 400 ProLiant BL 685c blade servers.

The NYSE and its subsidiaries conduct trading in the United States and five European countries. Its subsidiary trading companies include the U.S. online trader NYSE Arca Options; Euronext trading in Belgium, France, the Netherlands, Portugal, and the United Kingdom; the Euronext commodities trading arm Liffe; and Alternext, an equity trading firm for small and medium-sized businesses in countries covered by Euronext. These companies trade equities, bonds, options, derivatives, and other securities. NYSE Euronext lists the stocks of about 4,000 companies and constitutes the largest trading organization in the world, its spokesmen said.

Rubinow said NYSE Euronext investigated two competing Linuxes and chose Red Hat on the basis of its technical support.