http://www.itworld.com/open-source/193823/how-linux-mastered-wall-street

Financial exchanges need their servers to execute trades as quickly as possible. Even an edge of a few milliseconds could, over the course of trading billions of dollars a day, provide a competitive edge.

One key attribute was the TCP/IP stack, the configuration of which determines how fast a message can be passed between two systems. Another appealing attribute has been a revamped scheduler, which ensures that a process — one performing a trade for example — isn’t interrupted once it has been started.