Mac OS X   Mac OS X Mac OS X  is a line of computer operating systems developed, marketed, and sold by Apple Inc, the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original or "classic" Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessors Mac OS X is a Unix-based operating system, built on technology developed at NeXT between the second half of the 1980s and Apple's purchase of the company in early 1996. It received UNIX 03 certification following its 10.5 version on Intel processors. The first version released was Mac OS X Server 1.0 in 1999, and a desktop-oriented version, Mac OS X version 10.0 followed in March 2001. Since then, five more distinct "end-user" and "server" versions have been released, most recently Mac OS X v10.5 in October 2007. Releases of Mac OS X are named after big cats; for example, Mac OS X v10.5 is usually referred to by Apple and users as "Leopard". The server edition, Mac OS X Server, is architecturally very similar to its desktop counterpart but includes workgroup management and administration software tools that provide simplified access to common network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others. It is included with Apple's Xserve server hardware, but is designed to run on most of Apple's computer models. Apple also produces specialized versions of Mac OS X for use on three of its consumer devices, the Apple TV, the iPhone, and the iPod touch.