FreeBSD is used by many of the world's largest corporations, and busiest Internet sites. Yahoo!, Apache, Sony Japan, Netcraft, Weathernews, Supervalue. Apple chose FreeBSD over Linux as the Unix core for Mac OS X. According to Netcraft, nearly 2.5 million active sites use FreeBSD as a network server -- about one million more than Red Hat Linux . In the last year alone, about one million new FreeBSD hosts were counted by Netcraft, an incredible growth rate despite more media attention towards Linux. Several of the largest commercial banks in the world are using FreeBSD in their processing of business to business transactions. Combined, these systems process about 1.5 trillion U.S. dollars per year and growing. They are using X11, Apache, jails, Perl, and a lot of other free software. Factors that help: Stability Source availability for helping understand and fix problems that occur (having the source to the system helps you to understand why your application does not do what you expect) Good performance Easy hardware upgrade paths The application is spread over many servers. Need more power in one part? Add more FreeBSD boxes. PC hardware sometimes is less than perfect, but at PC hardware prices, hot spares are practical. BSD has existed since the late 1970's and was the testbed and reference implementation for TCP/IP. The Internet Software Consortium (ISC) uses FreeBSD exclusively for f-root domain servers (in 21 cities now, usually with 3 servers per city). Modern FreeBSD is extremely refined and mature. FreeBSD consistently places at the top of the "uptime" lists produced by Netcraft to measure the stability of the world's busiest websites. FreeBSD is frequently used as a platform for embedded networking devices, including products from IBM, Inktomi, Juniper Networks, GTA, and Network Alchemy - a Nokia Company. The Weather Channel uses FreeBSD to do realtime audio/video presentation in hundreds of locations across the US serving content to millions of cable and satellite customers. The BSD license makes these commercial embedded applications possible.