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Interrupts In Operating System

  Interrupt is the mechanism by which modules like I/O or memory may interrupt the normal processing by CPU. It may be either clicking mouse, draging cursor, printing a document etc, the case where interrupt is getting generated.

REQUIREMENT OF INTERRUPT :-
  External devices are comparatively slower thasn CPU. So if there is no interrupt, CPU would waste a lot of time waiting for external devices to match its speed with that of CPU. This decreases the efficiency of CPU. Hence, interrupt is required to eleminate these limitations.

ADVANTAGES :-
  • It increases efficiency of CPU.
  • It decreases the waiting time of CPU.
  • It stops the wastage og instruction cycle.
DISADVANTAGES :-
  CPU has to do a lot of work to handle interrupts, resume its previous execution of program.

An interrupt is a condition that halts the microprocessor temperoraily to work on different task and then return to its previous task. Interrupt is an event or signal that request to attension of CPU. This halt allows peripheral devices to access the microprocessor.

Whenever an interrupt occur the processor completes the execution of the current instruction and starts the execution of an interrupt service routine ( ISR) or Interrupt handler.

ISR is a program that tells the processor to what to do when the interrupt occurs. After the execution of ISR, control return back to main routine where it was interrupted.



Interrups are basically of two types :-
1. Hardware interrupt.
2. Software interrupt. 
  
1. Hardware interrupt :- 
   These interrupts are caused by any peripheral devices by sending a signal throush a specified pin to the microprocessor. These are two hardware interrupts in 8086 microprocessor :-

  a > NMI (Non-mascable interrupt) :- It is a single pin non-mascable hardware interrupt which cann't be disabled. It is highest priority interrupt in 8086 microprocessor.

b > INTR (Interrupt request) :- It provides a signal interrupt request and is activated by I/O port. This can be masked or delayed.


2. Software interrupt :-
     There are instructions that are inserted within the program to generate interrupts. There are 256 software interrupts in 8086 microprocesor.

   
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