Windows 1.0 BYTE demo

Microsoft Window Manager Demonstration 0.01 is the earliest build of Windows 1.0 and Microsoft Windows as a whole that is confirmed to exist. It was shown in the December 1983 issue of BYTE Magazine, though the build itself is much older and was already obsolete by the time the article was published as Microsoft had redesigned the user interface sometime prior to the official announcement on 10 November 1983, and the new UI had little in common with this early one.

The interface is very similar to Microsoft's DOS applications such as Word and Multiplan which were also released or in development at the time, with a command bar at the bottom of the screen, and featured overlapping windows that were later replaced by tiling windows. It remains unclear whether the build and applications demonstrated were actually fully functional or just cleverly crafted to create an illusion of a working system.

A picture of a disk containing this build was posted to Twitter by ReflectiaX on 9 March 2022.