PC hardware fundamentals: What does an IRQ (Interrupt Request) allow an interface card or peripheral device to do with respect to the CPU?

Introduction / Context:
In personal computer architecture, an IRQ (Interrupt Request) line is a critical signaling mechanism. It allows hardware devices such as keyboards, network cards, and storage controllers to notify the central processing unit (CPU) that attention is required immediately. Understanding the purpose of an IRQ helps technicians diagnose resource conflicts and optimize system responsiveness.

Given Data / Assumptions:

• The system uses a standard PC interrupt controller architecture (e.g., legacy PIC or APIC).
• Interface cards and onboard controllers can assert an IRQ line.
• The CPU executes normal code until an interrupt arrives.

Concept / Approach:

An IRQ is a hardware-level signal that temporarily halts normal CPU execution so that the processor can run a dedicated Interrupt Service Routine (ISR). This mechanism is more efficient than constant polling. The ISR performs minimal, time-critical work and defers longer tasks to lower-priority routines, improving overall throughput and latency.

Step-by-Step Solution:

Verification / Alternative check:

System monitoring tools show interrupt counts per device. Increased counts map to active devices, confirming that IRQs are used to request CPU service rather than to directly transfer bulk data.

Why Other Options Are Wrong:

• Pass data to the CPU to be processed: Data transfer is handled by programmed I/O or DMA; the IRQ merely signals attention.
• Pass data from one card to another: That is not the IRQ’s function.
• Pass data to the computer’s memory: That is the role of DMA or CPU-driven stores, not IRQ signaling.
• None of the above: Incorrect because an IRQ explicitly interrupts the CPU to request service.

Common Pitfalls:

Confusing IRQ signaling with DMA data movement; assuming interrupts always mean high CPU usage; forgetting priority and masking settings can delay or block interrupts.

Final Answer:

Interrupt the CPU to request service