Traps must be handled immediately, before you can continue with the instruction. Who should handle exceptions Except for system calls, the user program doesn't know the exception occurred. The code that does this is called the Exception Handler. The CPU operates in one of two modes, kernel or user mode. Some instructions are not available.
All instructions are available.
Some Vocabulary Interrupt request - the activation of hardware somewhere that signals the initial request for an interrupt. In most minds, when people think of a kernel, they think of critical portions of an operating system. Handler - the code of the exception handler. First, we need to add some more details to our computer sytem model. The instruction tells you which register is used.