OS X (/ˌoʊ ɛs ˈtɛn/), previously Mac OS X, is a series of Unix-based graphical interface operating systems developed, marketed, and sold by Apple Inc. It is designed to run exclusively on Mac computers, having been pre-loaded on all Macs since 2002. It was the successor to Mac OS 9, released in 1999, the final release of the "classic" Mac OS, which had been Apple's primary operating system since 1984. The first version released was Mac OS X Server 1.0 in 1999, and a desktop version, Mac OS X v10.0 "Cheetah" followed on March 24, 2001. Releases of OS X are named after big cats: for example, OS X v10.8 is referred to as "Mountain Lion". OS X, whose X is the Roman numeral for 10 and is a prominent part of its brand identity, is built on technologies developed at NeXT between the second half of the 1980s and Apple's purchase of the company in late 1996. The 'X' is also used to emphasize the relatedness between OS X and UNIX. Versions 10.5 "Leopard" running on Intel processors, 10.6 "Snow Leopard", and 10.8 "Mountain Lion" have obtained UNIX 03 certification. iOS, which runs on the iPhone, iPod Touch, iPad, and the 2nd and 3rd generation Apple TV, shares the Darwin core and many frameworks with OS X. An unnamed variant of v10.4 powered the first generation Apple TV.