ITPEC FE Morning April 2023 Question 17
ITPEC FE Morning April 2023 — Question 17 of 80
CPU Utilization with Interrupt-Driven I/O — calculate free CPU time during printing.
Given:
- Print speed: 400 characters/sec
- Each character triggers an interrupt: 50 μs
Step-by-step:
- Total interrupt time per second: 400 × 50 = 20,000 μs
- 1 second = 1,000,000 μs
- CPU busy ratio: 20,000 / 1,000,000 = 0.02 = 2%
- CPU available: 100% − 2% = 98%
Answer: (a) 98
Why not others:
- (b) 96 — would require 40,000 μs of interrupt time (double the actual)
- (c) 4 — confuses busy percentage with a smaller calculation error
- (d) 2 — this is the busy percentage, not the available percentage
Key rule: CPU available % = 100% − (interrupts_per_sec × time_per_interrupt) / total_time × 100%
AI-generated — may contain errors
The original exam layout is preserved in the image so diagrams, formulas, tables, and code remain accurate.
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official FE past-paper collection or Report an issue.