Which of following is NOT an open-source operating system?

Windows is correct.

Key Points

• Among the options, only Windows is NOT an open-source operating system.
• Windows is a closed source operating system marketed by Microsoft.
• Microsoft first introduced the Windows operating system on 20 November 1985.
• Closed Operating Systems are built with numerous codes and complex programming and that is called source code. 
• An Open-source Operating System is the Operating System in which source code is visible publically and editable.
• The operating system is a collection of programs that controls the overall operations of the computer.
• An operating system is a System software in computers.
• It works as an interface between the user and computer hardware components.
• Examples of operating systems are:
  • Linux.
  • Unix.
  • DOS.
  • Windows.
  • Ubuntu.
  • Embedded operating system.
  • OpenBSD.
  • Mac OS.

Mistake Points

Windows is an operating system, but it is NOT an open-source operating system.