A computer with interrupt?driven I/O has an interrupt response time of 4 ?s (i.e., it takes 4 ?s to invoke the interrupt handler and begin executing the target code). Similarly, it takes 2 ?s to return from the interrupt and begin executing the interrupted program.

a. If this computer executes 10 instructions per microsecond and the interrupt handler is 10 instructions long, how efficient is interrupt handling?
b. If interrupt handling is approximately 80% efficient, how large should the interrupt handler be (in terms of instructions)?

a. efficiency = interrupt execution/(interrupt execution + call + return) = 100 instructions × 0.1 ?s/(100 × 0.1 ?s + 4 ?s + 2 ?s) =10?s/(10 + 6)?s = 10/16 = 0.625 = 62.5%

b. 80% = 0.8 = n × 0.1/(n × 0.1 + 4 + 2). = n/(n + 60) Therefore, 0.8n + 48 = n; n = 240