4. (a) Explain the three fundamental ways in which I/O can be performed and compare their benefits and drawbacks.

(b) For each of the three ways determine how much CPU time is needed to print a 1KB document. The initial set-up takes 20 milliseconds in each case. It takes 50 microseconds to put a character in the data register of the controller of the printer, and printing one character takes 50 milliseconds. Assume that each interrupt service procedure needed runs for 70 microseconds and that the data register of the controller of the printer can contain only one character..