<P> Graphical user interfaces evolve over time . For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 1999 . </P> <P> A real - time operating system (RTOS) is an operating system intended for applications with fixed deadlines (real - time computing). Such applications include some small embedded systems, automobile engine controllers, industrial robots, spacecraft, industrial control, and some large - scale computing systems . </P> <P> An early example of a large - scale real - time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System . </P> <P> Embedded systems that have fixed deadlines use a real - time operating system such as VxWorks, PikeOS, eCos, QNX, MontaVista Linux and RTLinux . Windows CE is a real - time operating system that shares similar APIs to desktop Windows but shares none of desktop Windows' codebase . Symbian OS also has an RTOS kernel (EKA2) starting with version 8.0 b . </P>

What are the different classification of operating system