File Systems

File Allocation Methods

Method	Advantages	Disadvantages
Contiguous	Fast sequential and direct access	External fragmentation; hard to grow files
Linked	No external fragmentation	Slow direct access; pointer overhead (FAT improves this)
Indexed	Direct access, no external fragmentation	Index-block overhead (UNIX inodes use multi-level indexing)

Directory Structures

Single-level, two-level, tree-structured, acyclic graph (shared files and links) and general graph.

Free-Space Management

Bit vector (bitmap), linked free list, grouping and counting.

UNIX inode

Text

inode: metadata (owner, permissions, size, timestamps)
       12 direct block pointers
       1 single-indirect pointer
       1 double-indirect pointer
       1 triple-indirect pointer

Linux File Permissions

Terminal

ls -l notes.txt
chmod 754 notes.txt     # rwx for owner, r-x for group, r-- for others

-rw-r--r-- 1 asha staff 120 Nov 6 10:15 notes.txt

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