What is Interrupt in OS?
An interrupt is a signal emitted by hardware or software when a process or an event needs immediate attention. It alerts the processor to a high-priority process requiring interruption of the current working process. In I/O devices, one of the bus control lines is dedicated for this purpose and is called the Interrupt Service Routine (ISR).
When a device raises an interrupt at the process, the processor first completes the execution of an instruction. Then it loads the Program Counter (PC) with the address of the first instruction of the ISR. Before loading the program counter with the address, the address of the interrupted instruction is moved to a temporary location. Therefore, after handling the interrupt, the processor can continue with the process.
While the processor is handling the interrupts, it must inform the device that its request has been recognized to stop sending the interrupt request signal. Also, saving the registers so that the interrupted process can be restored in the future increases the delay between the time an interrupt is received and the start of the execution of the ISR. This is called Interrupt Latency.
A single computer can perform only one computer instruction at a time. But, because it can be interrupted, it can manage how programs or sets of instructions will be performed. This is known as multitasking. It allows the user to do many different things simultaneously, and the computer turns to manage the programs that the user starts. Of course, the computer operates at speeds that make it seem like all user tasks are being performed simultaneously.
An operating system usually has some code that is called an interrupt handler. The interrupt handler prioritizes the interrupts and saves them in a queue if more than one is waiting to be handled. The operating system has another little program called a scheduler that figures out which program to control next.
