File Access

• The information stored in a file can be accessed in a variety of methods:
  • Sequential access
    • in order, one record after another
    • read all bytes/records from the beginning
    • cannot jump around, could rewind or back up
    • convenient when medium was mag tape
  • Random (Direct) access
    • bytes/records read in any order skipping the previous records
    • essential for data base systems
    • read can be
      • move file pointer (seek), then read or
      • each read specifies the file pointer
  • Keyed; in any order, but with particular value(s); e.g., hash table or dictionary. TLB lookup is one example of a keyed search
• Other access methods, such as indexed, can be built on top of the above basic techniques.