Part D

• A file system is an integral part of every OS, whose function is to implement the concept of files.
• A file is a named collection of information managed on secondary storage by the FS.
• A file can be viewed as an unstructured stream of bytes or a series of records.
• A record is a structure of related data items, possibly of different data types.
• Records are identified within a file by a record number or a unique key field.
• An access method is a set of operations provided by the OS as part of the user interface to access files.
• The most common access method is sequential
• Read/write n bytes is applicable to byte-oriented files
• Read/write record k is applicable to fixed-length record files
• Read/write next record is applicable to both fixed and variable length record files
• A seek is generally not necessary for fixed length record files
• A file header is a portion of the file preceding the actual data and is visible to only the FS itself.
•  A file extension is a sequence of one or more characters following the file name.
• The contents of a file created in MS Word can be displayed using Adobe Acrobat by _.

  1. changing the file extension from .docx to .pdf
  2. opening the .docx file in Word and storing contents in a .pdf
  3. changing the files magic number to indicate a pdf format
  4. Answer: 2
• An MS Word file test.docx, containing the text 'Testing', is renamed by the user to test.txt. Under weak file type enforcement, double-clicking the file _.

  1. invokes Word; displays "Testing" as formatted
  2. invokes text editor; displays "Testing" as formatted
  3. invokes text editor; displays unreadable characters
  4. Answer: 3
• The magic number is a short sequence of characters at the start of the file header, which identifies the file type.
• A file directory (or folder) is a special-purpose file that records information about other files and possibly other directories.
• A tree-structured directory hierarchy is a collection of directories organized such that (1) every directory points to zero or more files or directories at the next lower level, and (2) every file and directory except the root is pointed to by exactly one parent directory at the next higher level.
• The root of a tree-structured directory hierarchy is the highest level directory, which does not have a parent directory.
• An MS Word file test.docx, containing the text 'Testing', is renamed by the user to test.txt. Under strong file type enforcement, double-clicking the file:

  1. Invokes Word; "Testing" displayed
  2. Invokes text editor; "Testing" displayed
  3. Invokes text editor; unreadable characters displayed
  4. Answer: 1
• An absolute path name of a file, uniquely identified by an internal ID, f, is the concatenation of the directory and file names leading from the root to the file f.
• A relative path name is a concatenation of file names starting with the current directory.
• A File control block is a data structure associated with a filename that contains all relevant attributes of the file
• FCBs are stored apart from file directories and are pointed to by the corresponding directory entries.
• Keeping only the file name and an FCB pointer instead of all attributes in a directory entry is preferable when file names are very long (T or F)

  F
• Keeping only the file name and an FCB pointer instead of all attributes in a directory entry is preferable when attribute lists are very long (T or F)

  T
• Keeping only the file name and an FCB pointer instead of all attributes in a directory entry is preferable when file headers are very long (T or F)

  F
• Keeping only the file name and an FCB pointer instead of all attributes in a directory entry is preferable when the number of files per directory is very large (T or F)

  T
• The create file operation causes the creation of new named file
• The destroy file operation removes an existing file from the FS.
• The create operation must specify as a parameter the file name (T or F)

  T
• The create operation must specify as a parameter the file length (T or F)

  F
• The create operation must specify as a parameter the list of blocks to hold the files contents (T or F)

  F
• To avoid having duplicate file names, the create operation must search the current directory
• The destroy operation must search the directory for the file name (T or F)

  T
• The destroy operation must free the directory corresponding to the file (T or F)

  T
• The destroy operation must reset the file length to 0 (T or F)

  F
• The destroy operation must free all disk blocks currently allocated to hold the file's contents (T or F)

  T
• The destroy operation must set all pointers to disk blocks to NULL (T or F)

  F
• The open file table (OFT) is a data structure that keeps track of all files currently in use to facilitate efficient access to and manipulation of the files