3.3 Supervisor Mode, Exceptions, and Traps

In this section we consider exceptions and traps. These are mechanisms to handle internal conditions and they are very similar to interrupts in form. We begin with a discussion of supervisor mode, which some processors use to handle exceptional events and protect executing programs from each other.

3.3.1 Supervisor Mode

As will become clearer in later chapters, complex systems are often implemented as several programs that communicate with each other. These programs may run under the command of an operating system. It may be desirable to provide hardware checks to ensure that the programs do not interfere with each other—for example, by erroneously writing into a segment of memory used by another program. ...

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