Section 11.6: OS modes and instructions (Frame 5) [prev][home][next]

In some ways the operating system is merely a huge collection of subroutines. There is one for ending a job's existence. Another subroutine exists for sending and receiving messages and yet another for creating children programs and so forth. User programs call these subroutines when they need them, like any program calls a subprogram when it needs it. (Remember that the terms subroutine, subprogram, function and procedure are all synonymous in this discussion.) There must also be a tiny core of program in the OS that starts the whole system going but once it is going, it is more or less in the hands of the user programs. After all, OS's exist for the pleasure and benefit of the user programs, don't they?

ASIDE: If you have never seen the movie 1983 "Tron," you should. It is a fascinating visual joyride through the interior or a computer. The operating system is called the MCP, Master Controlling Program, and it acts like one! The main question that the inner components ask each other is "Do you believe in users?" "Tron" is a neat way to gain an appreciation of computer architecture.