Classic Microsoft Windows

Classic Microsoft Windows is a colloquial term used to describe a series of operating systems developed for IBM-compatible personal computers by Microsoft Inc. from 1985 until 2031. It was included with most computers that were sold during the era it was developed, and many updates to the system software were made.

Microsoft released Windows 1.0 on November 20, 1985. The first version of Windows was partially based on MS-DOS, previously released by Microsoft in 1981. The last major release of the system was Windows XI in 2025.

With the introduction of Windows NT 3.1, a non-DOS-based Windows-compatible line of enterprise operating systems started, and OSes for personal computing were later integrated into the NT line starting with Windows XP.

After two aborted attempts at creating a successor to Windows called Midori and Singularity, and a four-year development effort spearheaded by Bill Gates' return to Microsoft in 2027, Microsoft replaced Windows with a new operating system in 2031 named Windows Z. It retained most of the user interface design elements of the classic Windows, and there was some overlap of application frameworks for compatibility, but the two operating systems otherwise have completely different origins and architectures.

The final major updates to Windows XI released in 2031 provided interoperability with Windows Z. The name "Classic" that now signifies the historical Windows as a whole is a reference to the Classic Environment, a compatibility layer that helped ease the transition to Windows Z.