File System Simulation

CSC-264 · Semester IV · Operating Systems

intermediate30 minAvailable

File System & Block Allocation

Navigate the directory tree and watch files land on disk blocks.

readme.md— blocks

todo.txt— blocks

File name

Blocks

Disk blocks (32 × 4 KB)

1 free fragments

On-disk files

boot.sys(3 blocks)blocks 0–2

kernel.bin(6 blocks)blocks 3–8

user.db(4 blocks)blocks 9–12

doc.txt(2 blocks)blocks 13–14

media.mp4(5 blocks)blocks 15–19

Trade-offs

Contiguous is fast but suffers external fragmentation. Linked allocation uses free blocks anywhere but each block carries a pointer. Indexed allocation needs one index block per file but supports direct random access.

Lab brief

Objective

Simulate contiguous, linked and indexed file allocation on a block device and compare their space use and access behaviour.

Theory & concepts

Allocation methods differ in how the directory maps a file to its blocks. Contiguous allocation stores a start block and length; linked allocation chains blocks with pointers; indexed allocation keeps one index block per file. Each has different costs for random access and different fragmentation behaviour.

Rendering diagram…

Mapping a file name to disk blocks through the inode

Method	Directory entry	Random access	Waste
Contiguous	start, length	Instant	External fragmentation
Linked	first, last block	Walk the chain	Pointer per block
Indexed	index block pointer	One index lookup	Index block overhead

Prerequisites

Lesson: File allocation methods
Lesson: Free space management

Instructions

1Create files with sizes and names (or load the sample set).
2Run the simulation under each allocation method.
3Read the block map to see where each file's blocks landed.
4Compare total blocks used and identify fragmentation for each method.

Tasks

Contiguous allocation
Allocate the sample files and identify the largest free hole left.
Linked allocation
Allocate the same files and show the pointer chains.
Indexed allocation
Allocate and read one file's index block; explain direct access.
Compare waste
Rank the methods by blocks used for the same file set.

Self-check

Block allocations match the selected method's rules.
The student reads the block map correctly.
Trade-offs between the three methods are explained.

Environment

block device mapallocation method selectorfile creatorspace usage stats