《操作系统》B卷(2011)(2)

3. (10pts) Consider the following system snapshot using the data structures in the

Banker's algorithm, with resources R0, R1, and R2, and processes P0 to P4: Max Allocation Available Process R0 R1 R2 R3 R0 R1 R2 R3 R0 R1 R2 R3

7 0 2 1 4 0 0 1 3 2 2 1 P0

1 6 5 0 1 1 0 0 P1

3 3 4 6 1 0 4 5 P2

1 5 6 2 0 4 2 1 P3

2 4 3 2 0 3 1 2 P4

Using Banker's algorithm answer the following questions.

(1) What are the contents of the Need matrix? (2) Is the system in a safe state? Why?

(3) If a request from process P2 arrives for additional resources of (0,2,0,0), can the

Banker's algorithm grant the request immediately? Why? Show the new system state and other criteria.

《操作系统》试卷B 第 6 页 共 9 页

4. (10 pts) Consider a demand paging system with three frames. And the given page

reference sequence is A, D, B, E, A, E, F, G, A, G, E, F. How many page faults does each of the LRU, FIFO, and Optimal page replacement algorithms generate? (Show your work step-by-step. A simple answer will receive no credit.) 《操作系统》试卷B 第 7 页 共 9 页

5. (10 pts) A certain file system uses 2-KB disk blocks. And the i-nodes contain 8 direct

entries, one single and one double indirect entry each. The size of each entry is 4 B. Answer the following questions:

(1) What is the maximum file size of this file system?

(2) How much disk space a 128-MB file actually occupied? (including all the direct

and indirect index blocks) 《操作系统》试卷B 第 8 页 共 9 页

6. (10 pts) Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and

38, in that order. Assume that initially the disk read/write arm is at cylinder 20.

(1) Using Shortest Seek First (SSF) algorithm, give the order in which the cylinders

are serviced and the total cylinders the arm moves.

(2) Using elevator algorithm, give the order in which the cylinders are serviced and

the total cylinders the arm moves (initially moving upward).

《操作系统》试卷B 第 9 页 共 9 页

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