Consider a system employing interrupt-driven I/O for a particular device that transfers data at an average of 8 KB/s on a continuous basis. a. Assume that interrupt processing takes about 100 s (i. e., the time to jump to the interrupt service routine (ISR), execute it, and return to the main program). Determine what fraction of processor time is consumed by this I/O device if it interrupts for every byte.
b. Now suppose that the device has two 8-byte buffers. The CPU is interrupted when one of the buffers is full. While the interrupt is processed, the device continues to fill the second buffer so that no data is lost. The interrupt service routine now takes 14 μs for all its other functions except the data transfer. The ISR transfers 8 bytes, where the transfer of each byte from the device to the CPU takes 2 μs.
c. Now assume that the processor is equipped with a block transfer I/O instruction such as that found on the Z8000. This permits the associated ISR to transfer each byte of a block in only 2 s. Determine what fraction of processor time is consumed by this I/O device in this case.