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 (from the second half of the 1980s to Apple's purchase of the company in late 1996) in combination with technologies from Apple's 'classic' OS and technologies from FreeBSD. OS X was rebranded macOS by Apple in 2016. It is the successor to Mac OS 9, the final release of the 'classic' Mac OS, which had been Apple's primary operating system since 1984.
Since 2002, Mac OS X has been included with all new Macintosh computer systems. OS X (pronounced oh ess ten) is the brand name of a series of Unix-compatible operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc.
