The first operating system for the Macintosh was System 1. It debuted with the original Macintosh on January 24, 1984, giving Apple's new computer its distinctive graphical desktop experience.
System 1 included the Finder, the menu bar, desktop accessories, a Clipboard, a Scrapbook, a Note Pad, and printer support. Because the original Macintosh had limited memory and no internal hard drive, it generally ran one main application at a time. The system itself occupied only about 216 KB.
The Macintosh operating system drew partly on ideas from Apple's Lisa OS and Xerox PARC's graphical-computing research. Its use of windows, icons, menus, and a mouse helped popularize the graphical user interface for personal computers.
There is a small historical naming wrinkle: the earliest Macintosh software did not originally have a distinct formal name and was often described as Macintosh System Software. Later histories conventionally identify the first release as System 1. It was followed by System 1.1 in December 1984 and then System 2.