Which Fortune 500 company created the Windows operating system?

Microsoft created the Windows operating system.

Microsoft introduced Windows 1.0 in 1985 as a graphical operating environment that ran on top of MS-DOS. It was not initially a complete replacement for DOS. Early Windows versions provided features such as overlapping or tiled windows, menus, icons, and support for applications designed for a graphical interface.

Windows eventually became Microsoft’s dominant personal-computer platform. Versions including Windows 3.1, Windows 95, Windows XP, and Windows 10 helped establish the operating system as a standard in homes, schools, and workplaces. Microsoft also developed server, gaming, and business software alongside Windows.

Windows is sometimes incorrectly credited to IBM because IBM and Microsoft worked together on OS/2. However, Microsoft developed the Windows product line. Microsoft was founded in 1975 by Bill Gates and Paul Allen, years before Windows first appeared.