Microsoft windows operating systems consists of a string of software operating systems updated to keep in line with new technologies and meet new and changing requirements of users. Microsoft released its first operating system in 1985 named 'Windows'. It was developed as an add-on to the MS-DOS operating system to meet the increasing need for a graphical user interface (GUI).

The earliest version of 16 bit windows operating system was thought to be just a graphical user interface. But in fact it already carried out many functions of typical operating systems by possessing their very own executable file format. It also provides its own device drivers for applications. Windows was also acceptable users to execute many graphical applications simultaneously (multitasking) unlike MS-DOS. 16-bit Windows versions comprises of Windows 1.0, Windows 2.0, Windows/286-Windows/386.

Windows/386 can also be categorized as an operating environment of Hybrid 16/32-bit. Windows3.0 and Windows 3.1 also falls under the category of Hybrid 16/32-bit operating environments. These operating systems had improved its design greatly because of loadable virtual device drivers and virtual memory, which provided facilities for sharing devices among multitasked DOS windows. Windows applications were now also able to execute in protected mode, making it possible to access many megabytes of memory and had no obligations like earlier systems to be involved in software virtual memory method.

Windows introduced for Workgroups 3.11 the 32-bit Windows operating system, with which it eliminated relying on DOS for file management. With this step, Microsoft released Windows 95 which supported lengthy file names. MS-DOS came inbuilt with Windows. Also the operating systems in this category were able to run 32-bit multitasked multi-threaded graphical programs, but as it was necessary to be compatible with 16-bit programs GUI components had to be 16-bit, not fully modified, resulting in low stability and performance. Three releases of Windows 95 (1995-1997), Windows 98 (1998), Windows 98 2nd edition (1999) and windows Me (2000) all falls under this category.

Windows NT operating systems falls under operating systems of 32-bit. These were distributed with higher reliability for business use. These were the first to put into practice the 'Windows 95' user interface and to include Windows 95's built-in 32 bit runtimes. Microsoft also introduced Windows XP which came in both home and professional versions, combining the consumer and business operating systems. It had enhanced user experience, stability and supported backward compatibility. The newest categories of operating system are 64-bit operating systems, in which the earlier versions supported Itanium. From Windows XP in 2005 Microsoft dropped its support for Itanium.

This is a simple brief of Microsoft Windows. Microsoft windows has more in-depth details for it has a greater history than can be covered in a few number of pages.