Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 8 (Page No. 430)

Question

Suppose that a computer can read or write a memory word in $5 nsec.$ Also suppose that when an interrupt occurs, all $32$ CPU registers, plus the program counter and PSW are pushed onto the stack. What is the maximum number of interrupts per second this machine can process?

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Answer 1

An interrupt requires pushing 34 words onto the stack. Returning from the interrupt requires fetching 34 words from the stack. This overhead alone is 340 nsec. Thus the maximum number of interrupts per second is no more than about 2.94 million, assuming no work for each interrupt.