OS X is a series of Unix-based graphical interface operating systems (OS) developed and marketed by Apple Inc. It is designed to run on Macintosh computers, having been pre-installed on all Macs since 2002. Within the market of desktop, laptop and home computers, and by web usage, OS X is the second most widely used desktop OS after Windows - wikipedia 
Launched as Mac OS X in 2001, it is the successor to the "classic" Mac OS, the final release of which was OS 9 from 1999, which had been Apple's primary operating system since 1984. The first version released was Mac OS X Server 1.0 in 1999; a desktop version, Mac OS X Cheetah followed in March 2001. In 2012, the software was renamed to OS X. Releases were named after big cats through OS X Mountain Lion; starting in 2013 with OS X Mavericks, they were named after California landmarks. The latest software version is OS X El Capitan, which was publicly released in September 2015. In June 2016, Apple announced the rebranding of the software to macOS starting with the upcoming release, macOS Sierra, giving the operating system a name similar to the names of Apple's other operating systems, iOS, watchOS, and tvOS.
OS X is based on technologies developed at NeXT between the second half of the 1980s and Apple's purchase of the company in late 1996. The X in "Mac OS X" and "OS X" is the Roman numeral for 10 and was a prominent part of its brand identity. It was also used to showcase UNIX compatibility; UNIX 03 certification was achieved for Intel CPU's v.10.5, and 10.6 to 10.11. iOS, the mobile OS for the iPhone, iPod Touch, iPad, and the 2nd and 3rd generation Apple TV, tvOS, the OS for the 4th generation Apple TV, and watchOS, the OS for the Apple Watch, share the Unix-based core and many OS X frameworks. A v.10.4 variant powers the first-generation Apple TV. Apple also formerly issued a separate line for server computing.
The first releases of OS X from 1999 to 2006 can run only on the PowerPC-based Macs from the time period. After Apple announced shift to using Intel x86 CPUs from 2006 onwards, Tiger and Leopard were released in versions for Intel and PowerPC processors, but Snow Leopard dropped PowerPC support. Support for 32-bit Intel processors was dropped after Lion; it now runs exclusively on 64-bit Intel CPUs.
# See also * History * Description * Compatibility * Features * Release history * Updating methods * Reception * See also * References * External links