File systems

Summary

A file system defines how an operating system names, stores, locates, and tracks files on a storage device. It manages both file content and metadata.

Introduction

Files appear as simple names and folders, but storage devices hold blocks of bytes. A file system connects these two views.

Explanation

The file system records which storage blocks belong to a file and keeps metadata such as size, timestamps, type, and access rules. It tracks free space and directory relationships. A mount point makes one file system accessible at a location in the directory tree. File-system formats differ, so their limits and features differ too.

Real-world example

Connect names to blocks

directory entry: photo.jpg
metadata: size 6 KB, owner lee
data blocks: 41 → 92 → 93
free-space map: blocks still available

Code example

1. find free storage blocks
2. write file content
3. update metadata and directory entry
4. confirm the operation completed

Common mistakes

• Treating a folder name as the physical location of its bytes.
• Assuming all file systems support identical names, permissions, or maximum sizes.
• Removing storage while writes may still be buffered.

Quiz

Key takeaways

• File systems map logical names and files to storage blocks.
• Metadata describes files separately from their content.
• Mounting exposes a file system; safe removal protects pending work.