From Wikipedia:
Microsoft Flight Simulator X (pronounced "Microsoft Flight Simulator Ten," as in the roman numeral), also known FSX, is the latest version of Microsoft Flight Simulator after Flight Simulator 2004. It includes a graphics engine upgrade as well as compatibility with Windows Vista, having been marketed by Microsoft as the most important technological milestone in the series to date. It is the first version in the flight simulator series to be released on DVD-ROM.
Flight Simulator X marks the tenth version of the popular line of flight simulators. It was officially released to the US market on October 17, 2006. According to Microsoft's Web site for the game, a standard edition features everything from navaids to GPS and airways. It also includes 18 planes, 28 detailed cities, and 40 highly detailed airports. The deluxe version features 24 types of aircraft, and 38 highly detailed cities.