System 7 (codenamed "Big Bang" and sometimes called Mac OS 7) is a single-user graphical user interface-based operating system for Macintosh computers. It was introduced on May 13, 1991 by Apple Computer. It succeeded System 6, and was the main Macintosh operating system until it was succeeded by Mac OS 8 in 1997. Features added with the System 7 release included cooperative multitasking, virtual memory, personal file sharing, an improved user interface, QuickTime, and QuickDraw 3D.
"System 7" is often used generically to refer to all 7.x versions. With the release of version 7.6 in 1997, Apple officially renamed the operating system "Mac OS", a name which had first appeared on System 7.5.1's boot screen. System 7 was developed for the Motorola 68k processor, but was ported to the PowerPC after Apple adopted the new processor.