is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, Mac OS X has been included with all new Macintosh computer systems. It is 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.
Mac OS X, whose X is the Roman numeral for 10 and is a prominent part of its brand identity, is a Unix-based graphical operating system,
built on technologies developed at NeXT between the second half of the 1980s and Apple's purchase of the company in late 1996. From its sixth release, Mac OS X v10.5 "Leopard" and onward, every release of Mac OS X gained UNIX 03 certification while running on Intel processors.
The first version released was Mac OS X Server 1.0 in 1999, and a desktop-oriented version, Mac OS X v10.0 "Cheetah" followed on March 24, 2001. Releases of Mac OS X are named after big cats: for example, Mac OS X v10.7 is usually referred to by Apple and users as "Lion". The server edition, Mac OS X Server, is architecturally identical to its desktop counterpart, and includes tools to facilitate management of workgroups of Mac OS X machines, and to provide access to network services. These tools include a mail transfer agent, an LDAP server, a domain name server, and others. It is pre-loaded on Apple's Xserve server hardware, but can be run on almost all of Apple's current selling computer models.
Apple also produces specialized versions of Mac OS X for use on its consumer devices. iOS, which is based on Mac OS X, runs on the iPhone, iPod Touch,
iPad, and the 2nd generation Apple TV. An unnamed variant of Mac OS X powered the 1st generation Apple TV.