File Attributes

• When a file is named, it becomes independent of the process, the user, and even the system that created it. For instance, one user might create the file $example.c$, and another user might edit that file by specifying its name.

  Figure 1: Some possible file attributes.

  
• The table of Fig. 1 shows some of the possibilities, but other ones also exist. No existing system has all of these, but each one is present in some system.
  • The first four attributes relate to the file's protection and tell who may access it and who may not.
  • The various times keep track of when the file was created, most recently accessed and most recently modified.
  • The current size tells how big the file is at present.
• A file's attributes vary from one OS to another but typically consist of these:
  • Name.
  • Identifier. This unique tag, usually a number, identifies the file within the file system; it is the non-human-readable name for the file.
  • Type.
  • Location. This information is a pointer to a device and to the location of the file on that device.
  • Size. The current size of the file (in bytes, words, or blocks) and possibly the maximum allowed size are included in this attribute.
  • Protection. Access-control information determines who can do reading, writing, executing, and so on.
  • Time, date, and user identification. This information may be kept for creation, last modification, and last use.
• The information about all files is kept in the directory structure, which also resides on secondary storage. Typically, a directory entry consists of the file's name and its unique identifier.