By the mid-1990s, however, contemporary operating systems such as Windows NT, OS/2, and NeXTSTEP had all brought pre-emptive multitasking, protected memory, access controls, and multi-user capabilities to desktop computers. With the introduction of System 5, a cooperative multitasking extension called MultiFinder was added, which allowed content in windows of each program to remain in a layered view over the desktop, and was later integrated into System 7 as part of the operating system along with support for virtual memory. With the Switcher, the now familiar Clipboard feature allowed copy and paste between the loaded programs across switches including the desktop. The software of each loaded program used the memory exclusively only when activated by the Switcher did the program appear, even the Finder's desktop.

With the Macintosh 512K, a system extension called the Switcher was developed to use this additional memory to allow multiple programs to remain loaded. Initial versions of the System Software ran one application at a time. The last major release of the system was Mac OS 9 in 1999. That program ended after the release of Mac OS 8 in 1997.

Apple rebranded the system as Mac OS in 1996, starting officially with version 7.6, due in part to its Macintosh clone program. The name Macintosh System Software came into use in 1987 with System 5. This operating system consisted of the Macintosh Toolbox ROM and the 'System Folder', a set of files that were loaded from disk.

As part of an agreement allowing Xerox to buy shares in Apple at a favorable price, it also used concepts from the Xerox PARC Alto computer, which former Apple CEO Steve Jobs and other Lisa team members had previewed. The first version of the system software, which had no official name, was partially based on the Lisa OS, which Apple previously released for the Lisa computer in 1983. Apple released the original Macintosh on January 24, 1984.

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