计算机科学概论第十版第三章,计算机科学概论第10版-第3章答案

计算机科学概论第10版-第3章答案

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4. Interactive processing allows the user to communicate with a program during its execution. The phrase "real-time processing" means that the time required for the activities of the program being executed must coordinate with activities in the outside world.

5. An operating system that allows several activities to execute "at the same time."

6. Answers will vary. The goal is for students to "experience" multitasking so that it is real rather than theoretical. We wan them to connect material in the text with reality.

7. Answers will vary. They should project an understanding that application software reflects the computer's application, whereas utility software forms part of the system's infrastructure.

8. a. The shell of an operating system handles the communication with the operating system’s users. b. The kernel of an operating system performs the fundamental tasks of the system.

9. X is a directory containing the subdirectory Y, which contains the subdirectory Z.

10. A process is the execution of a program.

11. The status of each process (ready, waiting) and the priority of each process.

12. A process that is ready could make progress if given a time slice, but giving a time slice to a process that is waiting would merely waste time since it cannot progress until some event occurs.

13. Virtual memory is the memory space whose presence is merely simulated by swapping blocks of data back and forth between a disk and the memory actually present in the machine.

14. To create a 1024MB (MiB) virtual memory using 2KB (KiB) pages would require 524,288 pages.

15. If both processes merely need to read from the file, no conflicts will occur. However, if one of the processes is going to modify the file, them it should have exclusive access. (Such problems are discussed in Section 9.5 in the context of databases.)

16. Application software performs tasks that are unique to the use of the particular computer system, whereas system software performs tasks that are required as the software infrastructure of any computer system.

17. Load balancing refers to the task of keeping all the processors busy. Scaling has to do with dividing a task into subtasks that can be performed simultaneously.

18. The machine begins by executing a program, called the bootstrap, at a predetermined location in memory. This program directs the machine to load a program (the operating system) from mass storage into main memory. The original program tells the machine to transfer its attention to the program just loaded.

19. Since most of a computer's main memory is volatile, the operating system must be reloaded each time the machine is turned on.

20. Answers will vary. Most PCs give the user the option of altering parameters before the booting process actually begins--usually by pressing the F1 key. The software controlling this procedure is part of the BIOS stored in the machine's ROM. Students who have floppy drives will hear the bootstrap routine look for the operating system there before trying the hard drive. They should all be able to hear the bootstrap routine reading the operating system from the hard drive.

21. If the machine can execute 5 instructions in a microsecond, it can execute 5,000 instructions in a millisecond or 100,000 instructions in a 20 millisecond time slice. (The point is that a modern machine can do a lot in a single time slice.)

22. The typist would be typing 5 characters per second, or one every 200 milliseconds. Thus, 10 time slices could be allocated during the 200 milliseconds between characters.

23. At least half. This does not include the time required to actually transfer the data. 25 milliseconds = 25000 microseconds. Thus, 250,000 instructions could be executed during this time.