In computer hardware and operating systems, what is an interrupt and how does it affect normal program execution?

Introduction / Context:
Interrupts are a fundamental mechanism that allows hardware devices and software to get the attention of the CPU. Instead of the processor constantly polling devices to see whether they need service, devices can generate an interrupt signal when something important happens. The operating system responds by temporarily suspending the current program, handling the event, and then resuming normal execution. This question checks your understanding of this basic but powerful control concept.

Given Data / Assumptions:

• The CPU is executing a main program when an interrupt occurs.
• Interrupts may come from hardware devices or from software instructions.
• The operating system uses interrupt handlers or service routines to respond to these events.

Concept / Approach:
An interrupt is a signal to the processor that an event needing immediate attention has occurred. When the CPU receives this signal, it completes the current instruction, saves the context of the running program, and jumps to a special interrupt service routine. That routine handles the event, for example by reading data from an input device or acknowledging a timer expiry. After the service routine finishes, the CPU restores the saved context and continues running the original program from where it left off.

Step-by-Step Solution:
Step 1: Recognize that interrupts are not permanent failures but temporary diversions of control.Step 2: Note that an interrupt causes the CPU to pause the current sequence of instructions after the current instruction completes.Step 3: The CPU then vectors to an appropriate interrupt handler, which is part of the operating system or firmware.Step 4: After handling the event, the CPU returns to the interrupted program and resumes its normal flow.Step 5: Choose the option that describes an interrupt as a signal that temporarily halts normal execution so the CPU can service an urgent event.

Verification / Alternative check:
Common examples help verify this understanding. When you press a key on the keyboard, a hardware interrupt is generated to let the CPU know that input is available. Similarly, periodic timer interrupts allow the operating system to schedule multiple processes by time slicing. In each case, the running program is suspended briefly while the interrupt is serviced, then continued. This matched behavior confirms that the chosen description is correct.

Why Other Options Are Wrong:
Option B: Confuses interrupts with hardware failures. Interrupts are normal events, not permanent CPU stoppages.Option C: Suggests that interrupts run when the computer is off, which is impossible because the CPU is not executing any code at that time.Option D: Describes a type of memory or cache, which is unrelated to the control signal concept of an interrupt.

Common Pitfalls:
Students sometimes think that interrupts always come from hardware. In reality, software instructions such as system calls can also generate interrupts or similar traps. Another misunderstanding is that interrupts randomly break program execution. In well designed systems, interrupt handling is carefully controlled and deterministic, allowing real time events to be handled without losing program state.

Final Answer:
The correct answer is A signal that temporarily halts the normal execution of the current program so that the CPU can service an urgent event or request.