Operating System MCQs – Set 42

By Atul Sahu • Computer Science, Operating System

Operating System MCQs – Set 42

UGC NET Paper 2 Computer Science AUG 2016 – Operating System

821. Indexed allocation: file of 50 blocks, adding one block at end needs how many disk I/Os?

Operating System • File Systems • UGC NET Paper 2 Computer Science AUG 2016

A. 1 B. 101 C. 27 D. 0

822. LP max z=0.5x₂–0.1x₁ s.t. 2x₁+5x₂≤80, x₁+x₂≤20: maximum z = ?

Operating System • Linear Programming • UGC NET Paper 2 Computer Science AUG 2016

A. 6 B. 8 C. 10 D. 12

823. LP duality: (a) finite↔finite, (b) unbounded→infeasible, (c) both infeasible. Which?

Operating System • Linear Programming • UGC NET Paper 2 Computer Science AUG 2016

A. (a)&(b) B. (a)&(c) C. (b)&(c) D. (a),(b)&(c)

824. Linker tasks: I.Resolve externals II.Translate assembly III.Relocate IV.Access control. Which?

Operating System • Linkers • UGC NET Paper 2 Computer Science AUG 2016

A. (I,II) B. (I,III) C. (II,III) D. (I,IV)

825. With 8-page virtual, 4 frames, LRU, ref string … how many faults?

Operating System • Page Replacement • UGC NET Paper 2 Computer Science AUG 2016

A. 9 B. 10 C. 11 D. 12

826. Page-reference string with 5 frames: faults for LRU, FIFO, optimal are:

Operating System • Page Replacement • UGC NET Paper 2 Computer Science AUG 2016

A. 10,14,8 B. 8,10,7 C. 7,10,8 D. 7,10,7

827. Regarding UNIX “nice”: I. sets changes priority. II. nice value set at creation. III. takes command-line arg. Which?

Operating System • Process Control • UGC NET Paper 2 Computer Science AUG 2016

A. I, II only B. II, III only C. I, II, III D. I, III only

828. OS MTBF=30 days; MTTR=10 minutes. Availability ≈ ?

Operating System • Reliability • UGC NET Paper 2 Computer Science AUG 2016

A. 0.9697 B. 0.9797 C. 0.9901 D. 0.9997

829. Server up 75%, down 25%; how many replicas for ≥99% availability?

Operating System • Reliability • UGC NET Paper 2 Computer Science AUG 2016

A. 2 B. 4 C. 8 D. 16

830. Jobs A–E runtimes 9,6,3,5,x, 0 arrivals. For 3

Operating System • Scheduling • UGC NET Paper 2 Computer Science AUG 2016

A. B,A,D,E,C B. C,E,D,B,A C. E,D,C,B,A D. C,B,A,E,D
Answer: D. C,B,A,E,D
Explanation: Use SJF: runtimes 3(C),5(D),x,6(B),9(A). For 3

831. P1(20),P2(10),P3(30) arrive 1,3,7. SRTF context switches?

Operating System • Scheduling • UGC NET Paper 2 Computer Science AUG 2016

A. 2 B. 3 C. 4 D. 5
Answer: B. 3
Explanation: Preempt at t=3,7, finish P2→P1. Total CS count: 3 switches.

832. Unix kernel data: I. Process table always resident. II. u-structure swapped out if process not in memory. Which are correct?

Operating System • Unix Kernel • UGC NET Paper 2 Computer Science AUG 2016

A. Only I B. Only II C. Both I and II D. Neither
Answer: C. Both I and II
Explanation: The process table is kernel-resident; the per-process u-area can be swapped out when the process is inactive.

833. Paged VM: effective access time (μs) is:

Operating System • Virtual Memory • UGC NET Paper 2 Computer Science AUG 2016

A. 30 B. 34 C. 60 D. 68
Answer: B. 34
Explanation: Typical EAT = (hit_ratio×mem_access)+(miss_ratio×(mem_access+page_fault)), here ≈34 μs.

834. Scheduler re-evals priority ∝ waiting time, no I/O, all arrive at 0. Which?

Operating System • CPU Scheduling • UGC NET Paper 2 Computer Science AUG 2016

A. Priority B. Round Robin C. SJF D. FCFS
Answer: A. Priority scheduling
Explanation: A pure priority algorithm adjusts priorities by wait time.

835. Which is NOT true of cron daemon?

Operating System • Daemons • UGC NET Paper 2 Computer Science AUG 2016

A. Runs scheduled commands B. Starts at boot C. Reads crontab files D. User crontabs not stored
Answer: D. User crontabs not stored
Explanation: User crontabs are stored under spooled crontab files.

836. Given 4 processes, 12 instances of R, max needs & allocations given, is system safe? Safe sequence?

Operating System • Deadlock – Banker’s Algorithm • UGC NET Paper 2 Computer Science AUG 2016

A. No B. Yes,P1P2P3P4 C. Yes,P4P3P1P2 D. Yes,P2P1P3P4
Answer: C. Yes,P4P3P1P2
Explanation: Banker’s algorithm shows available resources satisfy P4→P3→P1→P2 in sequence safely.

837. Disk head at 32; FCFS queue 98,37,14,124,65,67. Total moves?

Operating System • Disk Scheduling – FCFS • UGC NET Paper 2 Computer Science AUG 2016

A. 320 B. 322 C. 321 D. 319
Answer: D. 319
Explanation: Seek sequence: 32→98(66)+98→37(61)+… sums to 319 tracks.

838. Null RPC=1 ms +1.5 ms per 1K. Read 32K as 32 RPCs takes ?

Operating System • Distributed Systems: RPC • UGC NET Paper 2 Computer Science AUG 2016

A. 49 ms B. 80 ms C. 48 ms D. 100 ms
Answer: A. 49 ms
Explanation: 32×(1+1.5)=32×2.5=80ms? Actually 1ms+1.5×1=2.5ms per K→32×2.5=80ms; but if null per call=1ms+1.5ms=2.5ms×32=80ms. Choice B.

839. Mode 641: owner rw, group r, others x; Mode 100: owner x only. Which correct?

Operating System • File permissions • UGC NET Paper 2 Computer Science AUG 2016

A. Only I B. Only II C. Both D. Neither
Answer: C. Both
Explanation: Permissions match both descriptions.

840. In UNIX, which `mkdir` creates subdirs `PIS/progs` and `PIS/data`?

Operating System • File System Commands • UGC NET Paper 2 Computer Science AUG 2016

A. mkdir PIS/progs PIS/data PIS B. mkdir PIS progs data C. mkdir PIS PIS/progs PIS/data D. mkdir PIS/progs data
Answer: C. mkdir PIS PIS/progs PIS/data
Explanation: First make PIS, then its children with full paths.

Disclaimer for MCQ Quiz
This quiz is for educational purposes only…

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Operating System MCQs – Set 42

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