OS X ( /oʊ ˌɛs 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", 10.7 "Lion" 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.

OS X originally ran on PowerPC-based Macs. In 2006, the first Intel Macs had a specialized version of 10.4 "Tiger". In 2007, 10.5 "Leopard" was the first to run on both PowerPC and Intel Macs with the use of Universal Binaries. 10.6 "Snow Leopard" was the first version of OS X to drop support for PowerPC Macs. Mac OS X 10.7 "Lion" was the first version of OS X to drop support for 32-bit Intel processors and run exclusively on 64-bit Intel CPUs.

The server edition, OS X Server, was architecturally identical to its desktop counterpart, and included tools to facilitate management of workgroups of OS X machines, and to provide network services. Starting with v10.7 "Lion", OS X Server is no longer offered as a separate operating system product; instead, the server management tools are available for purchase separately, and are preloaded on the server models of Mac Pro and Mac Mini along with OS X.

Part of a series on
  • History
  • Transition to Intel processors
  • Architecture
  • Technologies
  • List of applications
  • List of games
  • Components
  • Hera (1.0)
  • Kodiak (Public Beta)
  • Cheetah (10.0)
  • Puma (10.1)
  • Jaguar (10.2)
  • Panther (10.3)
  • Tiger (10.4)
  • Leopard (10.5)
  • Snow Leopard (10.6)
  • Lion (10.7)
  • Mountain Lion (10.8)
  • Address Book
  • Automator
  • Calculator
  • Calendar
  • Chess
  • Contacts
  • Dashboard
  • Dictionary
  • DVD Player
  • FaceTime
  • Finder
  • Grapher
  • iTunes
  • Mac App Store
  • Mail
  • Messages
  • Photo Booth
  • Preview
  • QuickTime
  • Safari
  • Stickies
  • TextEdit
  • Activity Monitor
  • AirPort Utility
  • Archive Utility
  • Audio MIDI Setup
  • Bluetooth File Exchange
  • ColorSync
  • Console
  • Crash Reporter
  • DigitalColor Meter
  • Directory Utility
  • DiskImageMounter
  • Disk Utility
  • Font Book
  • Grab
  • Help Viewer
  • Image Capture
  • Installer
  • Keychain Access
  • Migration Assistant
  • Network Utility
  • ODBC Administrator
  • Remote Install Mac OS X
  • Screen Sharing
  • System Preferences
  • System Profiler
  • Terminal
  • Universal Access
  • VoiceOver
  • Mac OS
  • Copland
  • Rhapsody
  • Darwin

Read more about OS X:  History, Description, Features, Versions