A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. The head is moving towards higher cylinders. What is the total head movement under LOOK scheduling?
Correct answer B. 280 cylinders
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Operating Systems MCQs
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A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. The head is moving towards higher cylinders. What is the total head movement under SCAN, which goes to the end of the disk before reversing?
Correct answer A. 318 cylinders
A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. What is the total head movement under SSTF scheduling?
Correct answer B. 230 cylinders
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Processes P0 to P3 share resources A, B and C. Allocation: P0 (1,0,1), P1 (2,1,1), P2 (1,0,2), P3 (0,1,0). Maximum: P0 (3,2,2), P1 (3,2,2), P2 (2,1,3), P3 (1,2,2). Available: (1,1,1). Which is a safe sequence under the Banker’s algorithm?
Correct answer B. P1, P0, P2, P3
Under the Banker’s algorithm, a process has Maximum demand (7, 5, 3) and currently holds Allocation (0, 1, 0). What is its Need vector?
Correct answer C. (7, 4, 3)
Three processes share identical units of one resource type, and each may need up to 4 units. What is the minimum number of units that guarantees deadlock cannot occur?
Correct answer B. 10
What is the relationship between a safe state and deadlock?
Correct answer A. A safe state is never deadlocked, but an unsafe state may lead to deadlock without being one yet
Requiring every process to request resources in a fixed increasing order of resource numbers prevents deadlock by eliminating which condition?
Correct answer B. Circular wait
Which graph does deadlock detection use when every resource has a single instance?
Correct answer C. A wait-for graph obtained by removing resource nodes from the resource-allocation graph
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What is the purpose of a translation look-aside buffer (TLB)?
Correct answer A. To cache recent page-number to frame-number translations so most lookups avoid an extra memory access
Which kind of fragmentation does paging suffer from?
Correct answer C. Internal fragmentation in the last page of a process
Which technique removes external fragmentation by shuffling memory contents so that all free space forms one large block?
Correct answer B. Compaction
Free memory holes of 150, 450, 250, 350 and 600 KB lie in that order. Under best fit, which hole is chosen for a 230 KB request?
Correct answer B. 250 KB
A system uses 32-bit logical addresses and a page size of 4 KB. How many bits form the page number?
Correct answer B. 20
With a page size of 1024 bytes, logical address 3500 is in a page mapped to frame 7. What is the physical address?
Correct answer C. 7596
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A 32-bit system with 4 KB pages uses a single-level page table with 4-byte entries. How large is each process’s page table?
Correct answer A. 4 MB
A TLB lookup takes 10 ns, a memory access takes 100 ns and the TLB hit ratio is 90 percent. What is the effective memory access time with a single-level page table?
Correct answer A. 120 ns
Under demand paging, memory access time is 100 ns, servicing a page fault takes 5 ms, and the page-fault rate is 0.0002. What is the effective access time, approximately?
Correct answer B. 1.1 microseconds
In segmentation, what happens if the offset in a logical address is greater than or equal to the segment’s limit?
Correct answer C. The hardware traps to the operating system with an addressing error
What does demand paging do when a process starts running?
Correct answer D. It loads a page into memory only when that page is first referenced