Interrupts

A hardware interrupt is when it causes the processor to save the current instruction and work momentarily and sends a command to deal with the interrupt before continuing with anything else as it has a higher priority that needs to be responded to. A good analogy is boarding an airplane for a trip. When you arrive at the airport you first need to go through ticketing. Without a ticket, you cannot go any further. An interrupt service routine, or ISR is a software routine that hardware invokes in response to an interrupt. Interrupt service routine examine an interrupt and determine how to deal with it. If no further handling is required because the device is disabled or the data is buffered, an ISR notifies the kernel. An ISR must perform quickly to avoid slowing down the command of the device and the operation of all lower priority interrupts, this can cause the computer to respond with a delay or slowly if the ISR cannot respond fast enough.