Directories

Approach 1: Single directory for entire system

• Put directory at known location on disk
• Directory contains <name, inumber> pairs
• Can’t have the same name for files

Approach 2: Single directory for each user

• Still slow

Approach 3: Hierarchical name spaces

• Allow directory to map names to files or directories
• File system forms a tree

Hierarchical UNIX

Structure

Directory contents are broken into 512 byte chunks

• Each chunk has direct structure
  • 32 bit i-number
  • 16 bit size of directory entry
  • 8 fit file type
    • e.g. directory, file
  • 8 bit length of file name
• Coalesce when deleting
  • If first direct in chunk deleted, set i-number = 0
  • Don’t reuse entries, add to the end