File Structure; From OS's perspective

• Stream of Bytes (see Fig. 2)
  • OS considers a file to be unstructured
  • Simplifies file management for the OS
  • Applications can impose their own structure
  • Used by UNIX, Windows, most modern OSes
• Records (see Fig. 2)
  • Collection of bytes treated as a unit; Example: employee record
  • Operations at the level of records (read_rec, write_rec)
  • File is a collection of similar records
  • OS can optimize operations on records
• Tree of Records (see Fig. 2)
  • Records of variable length
  • Each has an associated key
  • Record retrieval based on key

Figure 2: Three kinds of files. (a) byte sequence. (b) record sequence. (c) tree.