Interrupts
Virtually
all computers provide a mechanism by which other modules (I/O, memory) may
interrupt the normal processing of the processor.
Classes of Interrupts:
1. Program: Generated by some
condition that occurs as a result of an instruction execution, such as
arithmetic overflow, division by zero, attempt to execute an illegal machine
instruction and reference outside a user’s allowed memory space.
2. Timer: Generated by a
timer within in the processor. This allows the operating system to perform
certain functions on a regular basis.
3. I/O: Generated by an I/O
controller, to signal normal completion of an operation or to signal a variety
of error condition.
4. Hardware failure: Generated by a
failure , such as power failure or memory parity error.
Interrupts
are provided primarily as a way to improve processing efficiency. With
interrupts, the processor can be engaged in executing other instructions while
an I/O operation is in progress. From this point of the user program, an
interrupts is that; an interruption of the normal sequence of execution. When
the interrupt processing is completed, execution resumes. Thus, the user
program does not have to contain any special code to accommodate interrupts,
the processor and the operating system are responsible for suspending the user
program and then resuming it at same point.
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