MacOS succeeded the classic Mac OS, a Macintosh operating system with nine releases from 1984 to 1999. Within the market of desktop, laptop and home computers, and by web usage, it is the second most widely used desktop OS, after Windows NT. It is the primary operating system for Apple's Mac computers. MacOS ( / ˌ m æ k oʊ ˈ ɛ s/ previously Mac OS X and later OS X) is a proprietary graphical operating system developed and marketed by Apple Inc.