ITPEC FE Morning April 2020 Question 20
ITPEC FE Morning April 2020 — Question 20 of 80
Spooling & Job Scheduling — calculate total time for CPU execution + printing with a single printer.
Setup:
- CPU executes jobs sequentially by priority: A → B → C → D
- Printer prints each job after CPU finishes it, but only one job at a time (spooling queue)
- CPU and printer work in parallel
CPU timeline:
- A: 0–50, B: 50–80, C: 80–100, D: 100–140
Printer timeline (starts when CPU done AND printer free):
- A: 50–100 (CPU done at 50, printer free)
- B: 100–140 (CPU done at 80, printer busy until 100)
- C: 140–170 (CPU done at 100, printer busy until 140)
- D: 170–190 (CPU done at 140, printer busy until 170)
Answer: 190 seconds
Why not others:
- (a) 100 — only covers printing of job A
- (b) 160 — ignores printer queue wait times
- (d) 280 — sums all times without CPU/printer parallelism
Key rule: With spooling, CPU and printer overlap. The bottleneck is whichever device finishes last. Build both timelines to find the answer.
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