What is the difference betweeninterrupt-driven I/O versus pollingI/O

quote from:http://www.calvin.edu/academic/rit/webBook/chapter2/design/hardware/io/interrupts.htm

What is the difference betweeninterrupt-driven I/O versus pollingI/O?

Most inputand output devices are much slower than the CPU—so much slower thatit would be a terrible waste of the CPU to make it wait for theinput devices. For example, compare the speed you can type with thespeed the CPU can execute instructions. Even a very fast typistcould probably type no more than 10 characters per second, while amodern CPU can execute more than two billion instructions in thatsame second!

Polling
If the CPU simply waits for the next input character, we call thispolled I/O. In this method, the CPU continuously polls the I/Odevice in a program loop, waiting for the next input. Think of agame where a basketball player is asked to make as many free-throwsas possible in one minute, but the clock is down the hall inanother room. The player must run down the hall and check if theminute has passed, and if not, go back to the gym and try to makeanother shot, then run down the hall to check the clock and runback to take another shot. The player spends much of the timesimply checking (polling) the clock.

Interrupts
An alternative scheme for dealing with I/O is the interrupt-drivenmethod. Here the CPU works on its given tasks continuously. When aninput is available, such as when someone types a key on thekeyboard, then the CPU is interrupted from its work to take care ofthe input data. In our example, the basketball player would takeshots one after another, while a second person watched the clockdown the hall. When the clock reached one minute, the personwatching the clock would yell down the hallway for the player tostop. This allows the player to take many more shots, but at theexpense of needing someone to watch the clock. Similarly, the CPUcan work continuously on a task without checking the input devices,allowing the devices themselves to interrupt it as necessary. Thisrequires some extra "smarts" in the form of electronic circuitry atthe I/O devices so that they can interrupt the CPU.