Q. Why might a system utilize interrupt-driven I/O to manage a single serial port however polling I/O to manage a front-end processor such as a terminal concentrator?

Answer: Polling can be more proficient than interrupt-driven I/O. This is the situation when the I/O is frequent and of short duration. Although a single serial port will perform I/O relatively infrequently and should therefore use interrupts a collection of serial ports such as those in a terminal concentrator can produce a lot of short I/O operations as well as interrupting for each one could create a heavy load on the system. An opportune polling loop could alleviate that load without wasting many resources through looping with no I/O needed.