Directory - Files

📁 Files, Directories, and File Systems

Clean, GitHub‑friendly summary with structure, highlights, and visuals in mind.

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🗂️ 1. Files — Logical Data Containers

A file is a structured collection of data stored on secondary storage.

📌 File Contents

• Program code
• User data
• Metadata (attributes)

🏷️ File Attributes (Metadata)

| Attribute | Meaning | |———|——–| | Type | Executable, source, media, library | | Size | Current & maximum size | | Permissions | Read / Write / Execute | | Created Time | File creation timestamp | | Last Access | Last opened | | Last Modified | Last edit | | Owner | File creator | | Disk Location | Physical storage pointer |

⚙️ File Operations (System Calls)

create(), delete(), open(), close(), read(), write(), seek(), rename()

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📂 2. Directories — File Organization Structure

Directories organize files in a tree hierarchy.

🌳 Directory Structure

• Root directory: / or C:\
• Subdirectories nested under root

📍 Path Types

| Path Type | Example | |———|——–| | Absolute Path | /home/user/file.txt | | Relative Path | ../docs/file.txt |

📄 Directory Entry Stores

• File name
• File type
• Storage block pointer
• Metadata reference

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💽 3. File Systems — Disk Management Layer

A file system defines how files are stored, retrieved, and protected.

🧱 Disk Preparation

| Step | Purpose | |——|——–| | Partitioning | Divide disk into logical regions | | Formatting | Install file system structure |

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🧩 4. File Allocation Methods

📏 Contiguous Allocation

• File stored in continuous disk blocks
• Fast access
• ❌ Causes external fragmentation

🔗 Linked Allocation

• Each block stores pointer to next
• No fragmentation
• ❌ Slow random access

🗃️ Indexed Allocation

• Index block stores all file block addresses
• Fast random access
• Used in modern systems

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🧠 5. FAT File System (File Allocation Table)

• Based on linked allocation
• FAT stores all block links centrally
• Faster lookup if FAT cached in RAM

📦 Disk Layout

Reserved | FAT Table | Root Directory | Data Area

📄 Directory Entry Includes

• File name & extension
• Size
• Timestamps
• Starting block

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🐧 6. UNIX File System — i-node Architecture

Uses indexed allocation.

📌 i-node Stores

• File metadata
• Up to 15 block pointers

🧱 Block Pointer Levels

| Type | Purpose | |——|——–| | Direct Blocks | Store file data | | Single Indirect | Pointer list | | Double Indirect | Pointer‑to‑pointer | | Triple Indirect | Large file support |

Root directory location is always known.

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💾 7. Popular File Systems Comparison

File System	Platform	Features
FAT / exFAT	Portable	Simple, removable drives
NTFS	Windows	Security, journaling
EXT4	Linux	Stable, scalable
APFS	Apple	Optimized for SSD

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🧠 Developer Takeaways

✔ File allocation affects performance
✔ Indexed allocation improves random access
✔ Metadata enables security & ownership
✔ FAT = portable, NTFS = secure, EXT4 = scalable
✔ File systems manage fragmentation & disk efficiency