Module 2 Lesson 3: Repository structure (.git folder)

Every Git repository has a secret. This secret is a hidden folder called .git.

For most users, this folder is a "black box" that they should never touch. But for a Git Master, understanding this folder is the difference between "using Git" and "understanding Git." In this lesson, we peek under the hood.

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1. Where is it?

When you run git init or git clone, Git creates a .git directory at the root of your project.

• Working Directory: The files you see and edit.
• Git Directory: The hidden .git folder that tracks everything.

Crucial Rule: Never delete the .git folder unless you want to permanently erase the history of that repository and turn it back into a regular folder.

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2. Key Components of the .git Folder

If you open the .git folder, you will see several files and subdirectories. Here are the most important ones:

The config file

This is the repository-specific configuration file. It stores things like the URL of your remote repositories (GitHub/GitLab) and any special settings for this project.

The objects/ directory

This is the heart of Git. It is the database that stores the compressed content of every file, every commit, and every tree in your history. Every "object" is named with a unique SHA-1 hash (a 40-character string).

The refs/ directory

This stands for "references." It stores pointers to your commits.

• refs/heads/: Contains files named after your branches (like main). Inside each file is the SHA-1 hash of the most recent commit on that branch.

The HEAD file

The HEAD file is a special pointer that tells Git what you are currently working on. Usually, it points to a branch (e.g., ref: refs/heads/main). When you switch branches, Git simply updates this file.

The index file

As we learned in Module 1, this is your Staging Area. It’s a binary file that tracks what you have staged for your next commit.

graph TD
    Root[".git Folder"]
    Root --> Config["config (Settings)"]
    Root --> Objects["objects/ (Database)"]
    Root --> Refs["refs/ (Pointers)"]
    Root --> HEAD["HEAD (Current Branch)"]
    Root --> Index["index (Staging Area)"]
    
    Refs --> Heads["heads/ (Local Branches)"]
    Heads --> Main["main"]
    Heads --> Dev["feature-x"]

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3. How Git Stores Data (Snapshots, not Diffs)

Unlike older systems that only store the "changes" (diffs) between files, Git stores snapshots.

• If a file hasn't changed between versions, Git doesn't save a new copy; it simply creates a link to the previous version of the file that is already in its database. This makes operations like switching branches incredibly fast.

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Lesson Exercise

Goal: Inspect your local repository's "Brain."

1. Go to the git-practice folder you created in Lesson 1.
2. Open the .git directory.
3. Open the config file in a text editor.
4. Now, open the HEAD file. What does it say? (It likely says ref: refs/heads/main or master).
5. Open the description file. Does it contain anything useful? (Standard Git repos usually just have a placeholder here).

Observation: You'll see that Git is remarkably simple—it’s just a collection of text files and a compressed database that keeps track of your pointers.

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Summary

In this lesson, we established:

• The .git folder is the "Brain" and database of your project.
• objects/ is where the actual compressed content lives.
• refs/ and HEAD manage the "navigation" of your history and branches.
• config stores project-specific settings.

Next Lesson: We’ll learn how to keep the "Brain" clean by teaching Git which files it should ignore using .gitignore.