Lowering CPU Overhead with Interrupts

The invention that many engineers came upon years ago to improve this interaction between OS and a device, is something we’ve seen already: the interrupt. Instead of polling the device repeatedly, the OS can issue a request, put the calling process to sleep, and context switch to another task. When the device is finally finished with the operation, it will raise a hardware interrupt, causing the CPU to jump into the OS at a predetermined interrupt service routine (ISR) or more simply an interrupt handler. The handler is just a piece of operating system code that will finish the request (for example, by reading data and perhaps an error code from the device) and wake the process waiting for the I/O, which can then proceed as desired.

Improved utilization

Interrupts thus allow for overlap of computation and I/O, which is key for improved utilization. This timeline shows the problem: