Windows 1.0 was released on November 20, 1985, as the first version of the Microsoft Windows line. It runs as a graphical, 16-bit multi-tasking shell on top of an existing MS-DOS installation. It provides an environment which can run graphical programs designed for Windows, as well as existing MS-DOS software. Its development was spearheaded by the company founder Bill Gates after he saw a demonstration of a similar software suite known as Visi On at COMDEX.

Despite positive responses to its early presentations and support from a number of hardware and software makers, Windows 1.0 was received poorly by critics. Critics felt Windows 1.0 did not meet their expectations. In particular, they felt that Windows 1.0 put too much emphasis on mouse input at a time when mouse use was not yet widespread; not providing enough resources for new users; and for performance issues, especially on systems with lower computer hardware specifications. Despite these criticisms, Windows 1.0 was an important milestone for Microsoft, as it introduced the Microsoft Windows line. Windows 1.0 was declared obsolete and Microsoft stopped providing support and updates for the system on December 31, 2001.

Microsoft began developing a graphical user interface (GUI) in 1981. The development of Windows began after Microsoft founder Bill Gates saw a demonstration at COMDEX 1982 of VisiCorp's Visi On, a GUI software suite for IBM PC compatible computers. In 1983 Microsoft learned that Apple's own GUI software—based in part on Xerox PARC technology–was much more sophisticated, and decided that its own product would be different.

Microsoft first presented Windows to the public on November 10, 1983. Requiring two floppy disk drives and 192 KB of RAM, Microsoft described the software as a device driver for MS-DOS 2.0. By supporting cooperative multitasking in tiled windows when using well-behaved applications that only used DOS system calls, and permitting non-well-behaved applications to run in a full screen, Windows differed from both Visi On and Apple Computer's Lisa by immediately offering many applications. Unlike Visi On, Windows developers did not need to use Unix to develop IBM PC applications; Microsoft planned to encourage other companies, including competitors, to develop programs for Windows by not requiring a Microsoft user interface in their applications.

According to wikipedia