File Systems

This Galvin topic covers on-disk organisation. You compare allocation schemes (contiguous, linked, indexed/inode), understand how directories map names to files, analyse free-space management, and see how journaling protects metadata consistency across failures.

Relation 1 —

Write this relation with symbols exactly as in Operating System Concepts — Silberschatz, Galvin & Gagne before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in Operating System Concepts — Silberschatz, Galvin & Gagne before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

Write this relation with symbols exactly as in Operating System Concepts — Silberschatz, Galvin & Gagne before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

A file system must answer two questions efficiently: where are a file’s blocks, and which blocks are free. Contiguous allocation gives fast sequential access but suffers external fragmentation; linked allocation avoids fragmentation but is poor for random access; indexed/inode allocation stores block pointers in a per-file structure, balancing both and enabling direct access. Directories are themselves files that map human-readable names to inode numbers, decoupling naming from storage. Because a crash mid-update can corrupt metadata, journaling first writes intended changes to a log so recovery can replay or discard them, keeping the file system consistent.

State assumptions explicitly before using any relation for file systems — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Operating Systems viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Operating Systems papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to file systems.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

File Systems appears in systems software and backend. In Indian it software curricula this topic is tested because it connects theory to process, memory, and file management.

GATE and semester exams often combine file systems with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use file systems?" — answer with a lab, mini-project, or plant visit example if possible.

Students confuse the inode (metadata and block pointers) with the directory entry (name-to-inode mapping), and think journaling always logs file data (usually just metadata by default). Mixing up the trade-offs of contiguous, linked and indexed allocation is common.

Before attempting file systems problems, confirm you can:

1. FAT versus inode-based allocation (ext4, NTFS)
2. Journaling logs metadata changes for crash recovery
3. Access methods: sequential, direct, indexed

Revise the solved examples in Operating System Concepts — Silberschatz, Galvin & Gagne and one previous-year GATE or university paper for this unit.