System 6 (also referred to as System Software 6) is a graphical user interface-based operating system for Macintosh computers. It was released in 1988 by Apple Computer and was part of the classic Mac OS line of operating systems. System 6 was shipped with various Macintosh computers until it was succeeded by System 7 in 1991. The boxed version of System 6 cost $49 when introduced. System 6 is classed as a monolithic operating system. It featured an improved MultiFinder, which allowed for co-operative multitasking.
Cooperative multitasking made its Macintosh debut in March 1985 with a program called Switcher by Andy Hertzfeld, which allowed the user to launch multiple applications and switch between them. Many programs and features did not function correctly with Switcher. Also, Switcher did not display windows of other applications beside the selected one. It was not included with the operating system, but was available from Apple for purchase separately. Both System 5 and System 6 had a feature called MultiFinder instead, which was much more mature and widely used in System 6. MultiFinder could be enabled or disabled, with a reboot. If disabled, the Finder would quit when the user launched another application, thus freeing RAM for it. If enabled, the system behaved as in the nowadays familiar multitasking tradition, with the desktop and windows of other applications in the screen's background.
System 6 was officially supported by Apple for many different machines, some of which were shipped with System 6. It may be that some Apple computers for which System 6 was not officially supported may nevertheless be able to run it, perhaps with limitations