Device driver: a plug-in to the OS which communicates with a particular i/o device.
When we have more processes running than we have CPU’s, the processes can’t literally all be running at the very same moment, so instead we need a mechanism to pre-empt a process as it runs on the CPU so that the OS can hand the CPU over to another process for it run a while. If this happens fast and often enough, human users get the illusion that the programs are running at the same time even though they are really taking turns.
Interrupts suspend the currently running process to run the interrupt handler and then run the scheduler, the OS code which decides which process gets to next use the CPU.
