Microsoft first released Windows in 1985, when Windows 1.0 introduced a graphical operating environment for MS-DOS computers.
Windows 1.0 launched on November 20, 1985. It was not a fully independent operating system in the modern sense; it ran as a graphical environment on top of MS-DOS. The release included tools such as a calculator, calendar, clock, control panel, Paint, and early versions of Notepad and Write.
The first version supported overlapping windows only in a limited way, and it was less successful than later releases. Windows 3.0, released in 1990, achieved much broader adoption, while Windows 95 later became a major consumer milestone.
A common mistake is dating Windows to Microsoft's founding in 1975 or to Windows 95. Microsoft existed for a decade before Windows appeared, and Windows 95 was a later product rather than the first release.