What is an interrupt?

An interrupt is a signal generated by either hardware devices or software components to interrupt the normal execution of a program and request immediate attention from the operating system. This mechanism allows devices and software to communicate with the operating system asynchronously and notify it about specific events or requests without continuously polling or waiting for a response.

When an interrupt occurs, it causes the processor to suspend the current program execution and transfer control to a specific interrupt handler or interrupt service routine (ISR), as shown in the diagram above.

Let's have a look at the type of interrupts.

Types of interrupts

The interrupts are classified into two types:

1. Hardware interrupts.

2. Software interrupts.

Hardware interrupts

Hardware interrupts are generated by external hardware devices to communicate with the operating system. These interrupts indicate specific events or conditions that require attention from the system. Examples of hardware interrupts include:

1. Timer Interrupts: Generated by a system timer or clock to indicate the expiration of a specified time interval. Timer interrupts are commonly used for scheduling tasks, measuring time intervals, and triggering periodic events.

2. I/O Interrupts: Generated by input/output devices, such as keyboards, mice, disk controllers, or network interface cards, to indicate the completion of an operation or a request for attention. For instance, when a key is pressed on a keyboard, an interrupt is generated to notify the operating system.

Note: In a multitasking operating system, a timer interrupt may be set to occur every 10 milliseconds. When it expires, an interrupt is generated, and the OS scheduler takes control to switch between different running processes.

Software interrupts

Software interrupts, also known as software exceptions, are generated by software components to communicate with the operating system or trigger specific actions.

Examples of software interrupts include:

1. System calls: A system call is generated by software programs to request specific functions provided by the operating system. System calls enable user-level applications to interact with privileged operating system functions, such as file operations.

2. Exceptions: These are generated by the processor in response to exceptional conditions or events. Examples of exceptions include division by zero, invalid memory access, or illegal instructions.

Note: A user program wants to read data from a file. It invokes a system call (e.g., "read()") to request the operating system to perform the file read operation on its behalf. This is a system call scenario for software interuppt.

Benefits of interrupts

Interrupts offer several benefits to computer systems, which contribute to their efficient and responsive operation. Let's explore them:

1. Responsiveness: Interrupts allow immediate response to external events or requests instead of continuously polling or waiting for events.

2. Asynchronous communication: Interrupts facilitate asynchronous communication between hardware devices, software components, and the operating system and allow them to notify the system about events without requiring continuous synchronization.

3. Multitasking and multithreading: Interrupts play a significant role in multitasking and multithreading environments. They allow the operating system to efficiently switch between tasks or threads, ensuring fair allocation of resources.

Conclusion

Interrupts play an important role in modern computing systems, enabling efficient and responsive operation. This article has explored the concept of interrupts, their types, benefits, and examples. Today, real-time systems, such as those used in industrial control, medical devices, or communication networks, heavily rely on interrupts to ensure timely and accurate processing.