Classic Mac OS

Classic Mac OS is a general term used to describe vintage Macintosh system software (Mac OS) before (and not including) Mac OS X. Modern versions of macOS will not run "Classic" software by default and will require an emulator to do so.

Release history
Major releases of the classic Mac OS:
 * System 1, released January 24, 1984
 * System 2, released April 1985
 * System 3, released January 1986
 * System 4, released January 1987
 * System 5, released October 1987
 * System 6, released April 1988
 * System 7, released May 13, 1991
 * Mac OS 8, released July 26, 1997
 * Mac OS 9, released October 23, 1999