Chapter 11 Exercises

For Exercises 1- 15, mark the answers true and false as follows: A. True B. False
|1. |A text file stores binary data that is organized into groups of 8 or 16 bits that are interpreted as characters. |
| |A |
|2. |A program written in a high-level language is stored in a text file that is also called a source file. |
| |A |
|3. |The type of a file determines which kinds of operations can be performed on it. |
| |A |
|4. |The current file pointer indicates the end of a file. |
| |B |
|5. |Sequential access and direct access take about the same amount of time to retrieve data. |
| |B |
|6. |Some operating systems maintain a separate read pointer and write pointer for a file. |
| |A |
|7. |UNIX file permissions allow a group of users to access a file in various ways. |
| |A |
|8. |In most operating systems, a directory is represented as a file. |
| |A |
|9. |Two files in a directory system can have the same name if they are in different directories. |
| |A |
|10. |A relative path is relative to the root of the directory hierarchy. |
| |B |
|11. |An absolute path and a relative path will always be the same length. |
| |B |
|12. |An operating system is responsible for managing the access to a disk drive. |
| |A |
|13. |The seek time is the amount of time it takes for the heads of a disk to reach a particular cylinder. |
| |A |
|14. |The shortest-seek-time-first disk scheduling algorithm moves the heads the minimum amount it can to satisfy a pending |
| |request. |
| |A |
|15. |The shortest-seek-time-first disk scheduling algorithm moves the heads the minimum amount it can to satisfy a pending |
| |request. |
| |B |

For Exercises 16 - 20, match the file extensions with the appropriate file. A. txt B. mp3, au, and wav C. gif, tiff, and jpg D. doc and wp3 E. java, c, and cpp

|16. |audio file |
| |B |
|17. |image file |
| |C |
|18. |text data file |
| |A |
|19. |program source file |
| |E |
|20. |word processing file |
| |D |

For Exercises 21 - 23 , match the symbol with its use. A. / B. \ C. ..

|21. |Symbol used to separate the names in a path in a Windows environment. |
| |B |
|22. |Symbol used to separate the names in a path in a Unix environment. |
| |A |
|23. |Symbol used to represent the parent directory in a relative path name. |
| |C |

Exercises 24 - 57 are problems or short-answer questions.
|24. |What is a file? |
| |A file is the smallest amount of information that can be written to secondary memory. It is a named collection of data, |
| |used for organizing secondary memory. |
|25. |Distinguish between a file and a directory. |
| |A file is a named collection of data. A directory is a named collection of files. |
|26. |Distinguish between a file and a file system. |
| |A file is a named collection of data. A file system is the operating system's logical view of the files it manages. |
|27. |Why is a file a generic concept and not a technical one? |
| |A file is just a named collection of bits (data) in storage. Because there are different operating systems, there are |
| |different technical views of a file. Because we are talking from the user's view not the implementation view, the |
| |concept is generic. |
|28. |Name and describe the two basic classifications of files. |
| |Text files: Files that contain text. Each byte is an ANSII character or each 2 types is a Unicode character. |
| |Binary files: The bytes in a binary file do not necessarily contain characters. These files require a special |
| |interpretation. |
|29. |Why is the term binary file a misnomer? |
| |All files ultimately are just a collection of bits, so why call one file type "binary?" In a binary file, the bits are |
| |not interpreted at text. A binary file would just be a stream of uninterpreted bits unless there is an interpretation |
| |provided. If a binary file is printed without interpretation, it looks like garbage. |
|30. |Distinguish between a file type and a file extension. |
| |A file type is a description of the information contained in the file. A file extension is a part of the file name that |
| |follows a dot and identifies the file type. |
|31. |What would happen if you give the name "myFile.jpg" to a text file? |
| |It depends on what application program you use to open the file. If you use a program that expects an image file, you |
| |would get an error. If you use a program that expects a text file, there would be no problem. |
|32. |How can an operating system make use of the file types that it recognizes? |
| |If you click on a file on your desktop and the OS recognizes the file type, then the appropriate application program can |
| |be called to open the file. If you are writing Java programs using an integrated environment, then the files saved in |
| |the IDE are tagged and clicking on a file automatically opens the file in the IDE. |
|33. |How does an operating system keep track of secondary memory? |
| |The OS maintains a table indicating which blocks of memory are free. The OS also maintains a table for each directory |
| |that contains information about the files in that directory. |
|34. |What does it mean to open and close a file? |
| |Operating systems keep a table of currently open files. The open operation enters the file into this table and places |
| |the file pointer at the beginning of the file. The close operation removes the file from the table of open files. |
|35. |What does it mean to truncate a file? |
| |Truncating a file means that all the information on the file is erased but the administrative entries remain in the file |
| |tables. Occasionally, the truncate operation removes the information from the file pointer to the end. |
|36. |Compare and contrast sequential and direct file access. |
| |Both sequential and direct file access find and access a record. In sequential access the file pointer begins at the |
| |beginning of the file and can only move in one direction. Thus sequential access is linear: The only record that can be |
| |accessed is the first or the one immediately following the last one accessed. In direct access the file pointer can be |
| |moved to any specific record and the data accessed from that place. |
|37. |File access is independent of any physical medium. |
| |a. How could you implement sequential access on a disk? |
| |Sequential access always accesses the next record. You implement sequential access on a disk by not giving the user an |
| |access command that takes a record address as a parameter. |
| |b. How could you implement direct access on a magnetic tape? |
| |Each record on a magnetic tape is conceptually numbered from the first to the last. Keep a counter of which record was |
| |read last. When a user gives an access command to read a specific record, if the record number is beyond the last record|
| |read, then records are read and skipped until the correct record is found. If the record number comes before the last |
| |record read, the tape is rewound and records are read and skipped until the correct record is found. |
|38. |What is a file protection mechanism? |
| |A file protection mechanism is one that an operating system implements that ensures the only valid users can access a |
| |particular file. |
|39. |How does Unix implement file protection? |
| |Unix implements file protection by associating with each file a 3x3 table in which the rows are Owner, Group, and World |
| |and the columns are Read, Write/Delete, and Execute. The contents of each cell in the table are boolean values meaning |
| |yes and no. For example, a yes in the cell (Owner, Execute) means that the owner of the file can execute it. A no in |
| |the cell (World, Write/Delete) means that permission to write or delete a file is not granted to anyone that is not the |
| |owner of the file or within a specified group. (Group is a list of those considered part of the group.) |
|40. |Given the following file permission, answer these questions. |
| |Read |Write/Delete |Execute |
|Owner |Yes |Yes |Yes |
|Group |Yes |Yes |No |
|World |Yes |No |No |

| |a. Who can read the file? |
| |Any one can read the file. |
| |b. Who can write or delete the file? |
| |The owner and members of the group can write or delete the file. |
| |c. Who can execute the file? |
| |Only the owner can execute the file. |
| |d. What do you know about the content of the file? |
| |Because the owner has permission to execute the file, it must contain an executable program. |
|41. |What is the minimum amount of information a directory must contain about each file? |
| |A directory must contain the file name, the file type, the address on disk where the file is stored, the current size of |
| |the file, and permission information. |
|42. |How do most operating systems represent a directory? |
| |As a file. |
|43. |Answer the following questions about directories. |
| |a. A directory that contains another directory is called what? |
| |parent directory |
| |b. A directory contained within another directory is called what? |
| |subdirectory |
| |c. The directory that is not contained in any other directory is called what? |
| |root directory |
| |d. The structure showing the nested directory organization is called what? |
| |directory tree |
| |e. Relate the structure in d to the binary tree data structure examined in Chapter 8. |
| |A directory tree and a binary tree are both hierarchical structures in which there is only one way to reach any subtree. |
| |The root directory is equivalent to the root of the binary tree. In a binary tree, each node can have none, one, or two |
| |child nodes. In a directory tree, each node can have any number of subdirectories. |
|44. |What is the directory called in which you are working at any one moment? |
| |working directory |
|45. |What is a path? |
| |A path is a text string that specifies the location of a file or subdirectory. |
|46. |Distinguish between an absolute path and a relative path. |
| |An absolute path is a path that begins at the root directory and includes all successive subdirectories. A relative path|
| |is a path that begins at the current working directory and includes all successive subdirectories. |
|47. |Show the absolute path to each of the following files or directories using the directory tree shown in Figure 11.4: |
| |a. QTEffects.qtx |
| |C:\WINDOWS\System\QuickTime\QTEffects.qtx |
| |b. brooks.mp3 |
| |C:\My Documents\downloads\brooks.mp3 |
| |c. Program Files |
| |C:\Program Files |
| |d. 3dMaze.scr |
| |C:\WINDOWS\System\3dMaze.scr |
| |e. Powerpnt.exe |
| |C:\Program Files\MS Office\Powerpnt.exe |
|48. |Show the absolute path to each of the following files or directories using the directory tree shown in Figure 11.5: |
| |a. tar |
| |/bin/tar |
| |b. access.old |
| |/etc/mail/access.old |
| |c. named.conf |
| |/etc/named.conf |
| |d. smith |
| |/home/smith |
| |e. week3.txt |
| |/home/smith/reports/week1.txt |
| |f. printall |
| |/home/jones/utilities/printall |
|49. |Assuming the current working directory is C:\WINDOWS\System, give the relative path name to the following files or |
| |directories using the directory tree shown in Figure 11.4: |
| |a. QTImage.qtx |
| |QuickTime\QTImage.qtx |
| |b. calc.exe |
| |..\calc.exe |
| |c. letters |
| |..\..\My Documents\letters |
| |d. proj3.java |
| |..\..\My Documents\csc101\proj3.java |
| |e. adobep4.hlp |
| |adobep4.hlp |
| |f. WinWord.exe |
| |..\..\Program Files\MS Office\Winword.exe |
|50. |Show the relative path to each of the following files or directories using the directory tree shown in Figure 11.5: |
| |a. localtime when working directory is the root directory |
| |/etc/localtime |
| |b. localtime when the working directory is etc |
| |localtime |
| |c. printall when the working directory is utilities |
| |printall |
| |d. week1.txt when the working directory is man2 |
| |../reports/week1.txt |
|51. |What is the worst bottleneck in a computer system? |
| |Transferring data to and from secondary memory is the worst bottleneck. |
|52. |Why is disk scheduling concerned more with cylinders than with tracks and sectors? |
| |Seek time (the time to find the right cylinder) is more time consuming than locating which track or which sector, so seek|
| |time is the time to minimize. |
|53. |Name and describe three disk scheduling algorithms. |
| |First-come, first-serve (FCSC): The requests are handled in the order in which they are generated. |
| |Shortest seek time first (SSTF): The request closest to the read/write heads is handled next. |
| |SCAN: The read/write heads move back and forth handling the closest in the direction in which they are moving. |
| |Use the following list of cylinder requests in Exercises 31 through 33. They are listed in the order in which they were |
| |received. |
| |40, 12, 22, 66, 67, 33, 80 |
|54. |List the order in which these requests are handled if the FCFS algorithm is used. Assume that the disk is positioned at |
| |cylinder 50. |
| |40, 12, 22, 66, 67, 33, 80 |
|55. |List the order in which these requests are handled if the SSTF algorithm is used. Assume that the disk is positioned at |
| |cylinder 50. |
| |40, 33, 22, 12, 66, 67, 80 |
|56. |List the order in which these requests are handled if the SCAN algorithm is used. Assume that the disk is positioned at |
| |cylinder 50 and the read/write heads are moving toward the higher cylinder numbers. |
| |66, 67, 80, 40, 33, 22, 12 |
|57. |Explain the concept of starvation. |
| |In the SSTF algorithm, it is possible for some requests never to be serviced because requests closer to the read/write |
| |heads keep being issued. |