High Quality Content by WIKIPEDIA articles! Mac OS X is the newest of Apple Inc.`s Mac OS line of operating systems. Although it is officially designated as simply "version 10" of the Mac OS, "version 9" had a completely different codebase, file system, design, and hardware support. Mac OS had been Apple`s primary operating system since 1984, and the family was backward compatible, so Mac OS X supported an emulated version 9 until version 10.5.