MacOS

macOS is a UNIX-based operating system that was developed by Apple. The "classic" Mac OS was introduced in 1984 alongside the first Macintosh and remained in primary use on Mac PCs until the introduction of Mac OS X in 2001.

The first ever officially released version of Mac OS, System 1, was released on January 24, 1984. It was renamed from System to Mac OS in version 7.6, which was released in 1997.

The first version under the name Mac OS X was Mac OS X Server 1.0, which was released on March 16, 1999. They started public beta on September 13, 2000 and revealed a redesigned Dock, a new menu bar, and new interface. Tiger was the first release to adopt Intel processors and x86 archeticture in general. Mac OS X was released on March 24, 2001 as version 10.0, then renamed to OS X in version 10.8, then to macOS in 10.12. The latest version of macOS was macOS 10.15, released on October 7, 2019.

All versions of Mac OS before macOS 10.12 "Sierra" (2016) are to be retroactively referred to as either "Mac OS X", "Classic Mac OS", or "OS X."

In June 22, 2020, macOS Big Sur (version 11) was revealed at the WWDC 2020. Prior to the announcement, it was released to developers. Big Sur is notable for being the first macOS version to support Apple M chips, Apple-designed processors marketed as Apple Silicon, and ARM-based CPUs.

Version History
Legend: Old version   Latest version   Latest preview version   Future release

Trivia

 * Apple makes their codenames public and has a new codename every version. They named macOS versions 10.0-10.8 after big cats. Since macOS 10.9, they have named their OS after California landmarks.