What are the interrupt stages and processing?

The instruction cycle in a computer system consists of three main stages: fetch, execute, and interrupt handling. When an interrupt occurs during program execution, the CPU must temporarily suspend its current task to handle the interrupt request efficiently.

If an interrupt occurs, it is indicated by an interrupt flag. The CPU will transfer control to the interrupt handler routine, which checks the type of interrupt and executes the appropriate function. Although this involves overhead, it is more efficient than having the CPU wait idle for I/O completion or other activities.

Interrupt Processing Stages

The interrupt handler follows a priority-based approach, activating the most critical activity first while deferring less urgent tasks for later processing.

Example − Network Data Arrival

When a block of data arrives on the network line:

• The kernel marks the presence of data (urgent part) and immediately returns CPU control to the previously running process.

• The remaining processing (moving data to buffer where the recipient will find it) can be handled later as a deferrable task.

Interrupt Vector

An interrupt vector is a table of pointers stored in memory at fixed locations. It contains the addresses of interrupt service routines for different interrupt types, allowing the CPU to quickly locate the appropriate handler for each interrupt.

Step-by-Step Interrupt Processing

Interrupt Processing Flow

Conclusion

Interrupt processing enables efficient multitasking by allowing the CPU to handle urgent events without continuously polling devices. The systematic save-and-restore mechanism ensures that interrupted processes can resume execution seamlessly, making interrupts a fundamental component of modern operating systems.