Question

A CPU with interrupt driven I/O is busy servicing a disk request. While the CPU is midway through the disk-service routine, another I/O interrupt occurs.
a. What happens next?
b. Is it a problem?
c. If not, why not? If so, what can be done about it?

Answer 1

Answer:

• Working scenario:

When a CPU is working with interrupt driven I/O scheme, it will control the I/O interrupt on the basis of priority. This means that interrupts with higher priority will be processed first and others will be processed later.

• Part (a)

When the CPU is busy servicing a disk request and another I/O interrupt occurs, the CPU will check the priority line (assigned during design phase) of both the interrupts and then decides the precedence from both of them.  

When the CPU gets ready to process the interrupt, an Interrupt Acknowledge signal (INTA) is sent back in return to interrupt signal (INT).

• Part(b)

Occurring of interrupts while the CPU is midway through the disk-service is not a problem. It can happen normally.

• Part (c)

Occurring of interrupts while the CPU is midway through the disk-service is not a problem, the CPU just picks the multiple interrupts checks the priority line and processes one of the multiple interrupts based on the highest priority matter.

i hope it will help you!