Skip to content

LSA 15: Describe Interrupts

Interrupts are signals sent to the CPU by hardware or software that indicate an event requiring immediate attention. They temporarily pause the current execution flow, allowing the CPU to handle the interrupting event before resuming its previous operations. This mechanism is essential for effective multitasking and responsiveness in computing systems.

Key Components of Interrupts

  • Interrupt Service Routine (ISR): When an interrupt occurs, control is transferred to a specific function known as the Interrupt Service Routine (ISR), which contains the code to handle the interrupt. After the ISR has executed, normal operations are resumed.

Types of Interrupts

  1. Software Interrupts: Software interrupts, also referred to as traps or exceptions, occur when a program requests a service from the operating system, typically through a system call. These interrupts can also arise from exceptional conditions, such as arithmetic errors (e.g., division by zero) or invalid memory access. Software interrupts allow applications to communicate with the OS for resource management and other functions.

  2. Hardware Interrupts: Hardware interrupts are generated by hardware devices, such as keyboards, mice, disk drives, and network cards. These devices are connected to the Interrupt Request Line (IRQ), which allows them to signal the CPU when they require attention. For example, when a key is pressed on a keyboard, a hardware interrupt is sent to the CPU, prompting it to read the input and process it accordingly.

Importance of Interrupts

  • Efficient Resource Management: Interrupts allow the CPU to respond promptly to events, ensuring that resources are managed effectively and that devices are not left waiting unnecessarily.

  • Improved System Responsiveness: By handling events as they occur, interrupts enable a system to remain responsive to user inputs and other critical activities.

  • Multitasking Capability: Interrupts facilitate multitasking by allowing the CPU to switch between processes efficiently, responding to various tasks as they arise.

Interrupts play a vital role in computer architecture by enabling efficient communication between the CPU and hardware or software events. Understanding how interrupts function and their types helps in designing systems that are responsive, efficient, and capable of handling multiple tasks concurrently.

Examples of Interrupts

Here are some common examples of interrupts in computing:

1. Keyboard Input

  • When a user presses a key on the keyboard, a hardware interrupt is generated. The keyboard sends a signal to the CPU, prompting it to read the key pressed and process the input accordingly.

2. Mouse Movement

  • Similar to keyboard input, when the mouse is moved or a button is clicked, it generates a hardware interrupt. This allows the operating system to update the cursor position or respond to user actions immediately.

3. Disk I/O Operations

  • When data is read from or written to a disk drive, hardware interrupts notify the CPU when the operation is complete. This allows the system to process the next task without waiting idly for the I/O operation to finish.

4. Timer Interrupts

  • Many operating systems use timer interrupts to manage multitasking. A timer generates interrupts at regular intervals, allowing the OS to regain control and switch between different processes, ensuring fair CPU time distribution.

5. Network Packet Reception

  • When a network interface card (NIC) receives a data packet, it generates an interrupt to alert the CPU. This allows the system to process incoming network data promptly and efficiently.

6. System Calls

  • When a program requests a service from the operating system (e.g., file access, memory allocation), it triggers a software interrupt. This allows the CPU to switch to kernel mode to execute the requested service.

7. Hardware Failures

  • Certain hardware components can generate interrupts to signal errors or malfunctions, such as overheating or power failures. The CPU can then respond by executing error-handling routines.

8. User-defined Interrupts

  • In some systems, applications can generate software interrupts based on specific conditions or events, allowing for custom handling of particular scenarios.

These examples illustrate how interrupts facilitate communication between hardware, software, and the CPU, enabling efficient and responsive system operation.