What are Interrupts and System Exceptions, and how does interrupt handling work in an OS?

• A. Interrupts are asynchronous events; exceptions are synchronous errors; OS saves context, routes to ISR, handles, then resumes; uses interrupt controllers
• B. Interrupts are synchronous; exceptions asynchronous
• C. Exceptions are non-fatal; interrupts always halt the system
• D. Interrupts bypass the OS

Answer: (A)

Interrupts are signals from hardware that arrive independently of the currently running code, so they can occur at any time and momentarily interrupt the running task. Exceptions are generated by the CPU as it executes instructions, usually because something went wrong or a special condition arose in the code; these are synchronous with the instruction stream that caused them. When either happens, the processor saves the current execution state (registers, program counter, status) so the original task can be resumed later. The OS (via the interrupt controller) then transfers control to the appropriate interrupt service routine or exception handler. The handler runs in privileged mode to perform the necessary work, and when finished, the system restores the saved state and resumes the interrupted task. Interrupt controllers manage which interrupt gets serviced, handle masking and priority, and can support nested handling so higher-priority events can interrupt lower-priority ones. This flow ensures hardware events are addressed promptly while preserving the ability to continue the original program afterward.