Answer from cs61c-av (Kenneth Wong 16192104) for Question 3
Polling, which is like having the system monitor the status of the mouse by reading signals from it, has a drawback of wasting a lot of proccessor time.  With polling, a device simply puts the information into a status register.  But the processor never knows when the I/O has completed an operation, and must continually check the register.  Thus the system is dramatically slowed down, because the processor is just so much faster than I/O device.