INTERRUPTS AND EXCEPTIONS

INTERRUPTS AND EXCEPTIONS

Interrupts and exceptions both alter the program flow. The difference between the two is that interrupts are used to handle external events (serial ports, keyboard) and exceptions are used to handle instruction faults, (division by zero, undefined opcode).

Interrupts are handled by the processor after finishing the current instruction. If it finds a signal on its interrupt pin, it will look up the address of the interrupt handler in the interrupt table and pass that routine control. After returning from the interrupt handler routine, it will resume program execution at the instruction after the interrupted instruction.

Exceptions on the other hand are divided into three kinds. These are Faults, Traps and Aborts. Faults are detected and serviced by the processor before the faulting instructions. Traps are serviced after the instruction causing the trap. User defined interrupts go into this category and can be said to be traps; this includes the MS-DOS INT 21h software interrupt, for example. Aborts are used only to signal severe system problems, when operation is no longer possible.

reference:
http://www.faqs.org/faqs/assembly-language/x86/general/part2/section-3.html