Microsoft Windows

Microsoft Windows is a family of Operating Systems developed by Microsoft. It currently uses the Windows Explorer shell.

First versions of Windows were an operating environment for DOS. Nowadays it is a full operating system.

Windows for DOS
During this time, Windows was a desktop environment for DOS, an OS inspired by CP/M. There is a dispute whether it can be considered an operating system. One side points on the fact that it did include it's own graphics drivers and program API, which OS's do aswell, however on the other side the argument is that it extensively used the MS-DOS API. Last version of this series is Windows:3.x:3.11:Workgroups.

Windows 9x
In 1995, Microsoft released Windows 95, which was based on the older Windows for DOS code, however it was a hybrid 16/32bit operating system, which made almost all existing Win32 applications able to run. Windows 95, because of its heritage, included MS-DOS, however many DOS apps were either entirely replaced with a Windows version (MS-DOS Shell could be considered one) or extended with Win32 code (Scandisk). Windows 9x, though, used MS-DOS essentially only as a bootstrapper. Windows ME was the last release of this series.

Windows NT
Windows NT (New Technology) is the current series of the Windows operating systems. It builts on the NT kernel (hence the name), originally intended to be used in OS/2 3.0 but the code has been rewritten for a new version of Windows after the Microsoft - IBM split. The first release was Windows NT 3.1, which was versioned such to make eventual customers not think that it has got less abilites than Windows 3.1, its DOS counterpart. With Windows XP, the NT series opened its doors to the home customers, replacing Windows 9x. The most recent version is Windows 8.1, with Windows 10 being currently in development.