What was the first version of Microsoft Windows?

The first version of Microsoft Windows was Windows 1.0. Released on November 20, 1985, it was a graphical operating environment that ran on top of MS-DOS rather than a fully independent operating system in the modern sense.

Windows 1.0 provided tiled windows, mouse support, and early versions of familiar utilities such as Calculator, Paint, Notepad, Clock, and Control Panel. Its windows could not overlap; that limitation was later removed in Windows 2.0. Microsoft had publicly demonstrated the project in 1983, when it was briefly known by the codename Interface Manager, but development delays postponed its release.

The original product went through releases numbered 1.01 to 1.04. Windows 1.04, released in 1987, added support for IBM PS/2 computers. The system was not an immediate commercial sensation and was eventually replaced by Windows 2.0, but it established the software foundation that Microsoft would develop into the dominant PC desktop platform.