 DSOS was designed to exploit these features.DSOS (Frailey, 1975) was one of the pioneering efforts in real-time operating systems.Incorporating many of the principles being introduced at the time in mainframe systems, such as semaphores, memory management, task management and software interrupts, it used a clever scheme to assure appropriate real-time performance while providing many services previously uncommon in the real-time domain (such as an orderly way to communicate with external devices and computer operators, multitasking, maintenance of records, a disciplined form of inter-task communication, a reliable real-time clock, memory protection, and debugging support).