斯坦福大学操作系统期末考试题英文Word文档格式.docx

1、23_/104_/1456 _/1678910Total_/140Raw Score : _/ 140 = _/ 1001） 20 Points DeadlockConsider the following snapshot of a system （P=Process, R=Resource） :AvailableRARBRCRDMaximum DemandP01P1P2P3P4Current AllocationAnswer the following questions using bankers algorithm:a） Calculate the Needs matrix:Needs

2、b） Is the system in a safe state? If so, show a safe order in which the processes can run.c） Can a request of one instance of RA by Process P0 be granted safely according to Bankers algorithm?2） 20 points Logical and Physical Address SpacesThe Kiwi memory architecture design team has a dilemma. The

3、team is considering several different memory configuration variations for an upcoming machine design. Consider the following designs （All memory accesses are in terms of bytes, and all are using paging techniques）:CharacteristicDesign 1Design 2Design 3Physical Memory Address Width8 bit16 bit32 bitLo

4、gical Address Width12 bit20 bit24 bitPage/Frame size in bytes16 bytes32 bytes64 bytesPage Table TypeSingleDouble a） 6 points For each design, list the maximum number of pages each process can access in logical address space.b） 6 points For each design, list the maximum number of frames in physical m

5、emory.c） 6 points For design 3, if the outermost page table holds 32 entries, how many bits are needed in the logical address to represent the outer page table? How many bits are used for representing the offset within a page? How many bits are needed in the logical address in order to represent the

6、 inner page table?3） 4+4+2= 10 points Page Replacement Given the following reference string:0 2 1 3 0 1 4 0 1 2 3 4 showa） Page faults occur during the processing of the reference scheme?b） The hit ratio is for each of the following policies in a pure demand paging system?c） What do you observe when

7、 you move from Scheme 1 to Scheme 2? Explain.Scheme 1: FIFO with three pages of main memoryScheme 2: FIFO with four pages of main memory4） 6+4+4= 14 points Address TranslationConsider a system where the virtual memory page size is 2K （2048 bytes）, and main memory consists of 4 page frames. Now consi

8、der a process which requires 8 pages of storage. At some point during its execution, the page table is as shown below:Virtual pageValid Physical pageNoYes61. List the virtual address ranges for each virtual page.2. List the virtual address ranges that will result in a page fault.3. Give the main mem

9、ory （physical） addresses for each of the following virtual addresses （all numbers decimal）: （i） 8500, （ii） 14000, （iii） 5000, （iv） 2100.Policy : _5） 20 points File System ImplementationSuppose a file system is constructed using blocks of 8 words each. In this system, a word has a length of 4 bytes.

10、The disk pack used to hold the file system consists of 32 blocks. The initial block （block 0） contains a directory entry. The directory entry contains the filename of a single file in this file system, and a pointer to the first I-node in block 1. The I-node structure is as follows （word, value）: Pe

11、rmission wordFile SizeDirect blockSingle-indirectDouble-indirectThe file contains 16 words of data: the first direct index points at block 31, and the second direct index points at block 29. Blocks 4,7,10,and 15 are marked bad. Assume that free blocks are allocated in logical order starting with blo

12、ck 0 and that write operations modify the file system 1 block at a time. What will the state of the system look like after 100 additional words are appended to the file （draw a block diagram showing the structure of the I-node and the blocks that are allocated）6） 16 points Disk SchedulingDisk reques

13、ts come into the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. Assume that the disk has 100 cylinders.A seek takes 6msec per cylinder moved. Compute the average seek time for the request sequence given above for 1. First-come, First-served2. Shortest Seek Time First （SSTF）3.

14、 LOOK （with the disk-arm initially moving towards higher number cylinders from lower number cylinders）4. C-SCANIn all the cases, the arm is initially at cylinder 20. 7） 10 points Security: Public Key EncryptionConsider the public key encryption defined by the RSA （Rivest, Shamir, Adelman） scheme. As

15、sume that the two starting primes are p and q are 3 and 7 respectively and determine the （nontrivial） private key and public key pairs according to the RSA scheme.8） 10 Points Networking: TCP/IPThe following flowchart shows the client and server portions of a TCP communication session. Fill in the e

16、mpty bubbles/boxes with the appropriate socket system call names.CLIENT SERVER9） 10 points Enduring Principles in System Design1. When a system gets complex in design what is a common solution to manage the complexity? Give an example.2. When you experience incompatibilities between system modules,

17、how will you solve this problem?3. What is a common data structure used to manage （the slots for） n resources?4. The data items such as inodes and files are typically located in external memory that is sluggish relative to the local main memory. How are the effective access times of these structures

18、 minimized?5. When a table maintaining a list of pointers grows unmanageably large how will you solve this problem so that （i） search times of the table is reasonable and （ii） only the region of interest in the table need to be in the memory?10） 10 points Nachos Operating Systems1. List the two main

19、 operations （methods） that have the potential for resulting in a page fault.2. Where is the address that caused the page fault stored?3. You incremented the PC after every system call you implemented? Why not for page fault system call?4. What is the purpose of Exec, Join and Exit system calls?5. Explain the above with an example.6. How would you control the access to a shared resource by multiple threads?