Understanding Git Internals: How Git Stores Data

Amaresh Pelleti

Most developers use Git every day without ever thinking about how it actually works under the hood. We type git commit or git push, but behind the scenes Git is managing a powerful object database that makes it fast, distributed, and resilient.

In this guide, we’ll break down Git’s internals in plain English, explain how it stores data, and show you some hands-on commands to explore it yourself.

1. Git Is a Key-Value Database

At its core, Git isn’t just a version control tool—it’s a key-value database.

  • Each piece of data (commit, file, tree, etc.) is stored as an object.
  • Each object is identified by a hash (SHA-1 by default, SHA-256 in newer versions).
  • That hash is the key, and the object is the value.

This means every version of your project is stored as immutable snapshots, making Git both reliable and tamper-resistant.

2. The .git Directory: Where the Magic Happens

When you run git init, Git creates a hidden .git folder. This is the entire repository.

Key parts inside .git:

  • objects/ → Stores commits, trees, and blobs.
  • refs/ → Pointers to branches and tags.
  • HEAD → Tells Git what branch/commit you’re currently on.
  • config → Repository configuration.

Try it yourself:

git init demo-repo
cd demo-repo
ls -a

You’ll see the .git directory created.

3. Git Objects: The Building Blocks

Git uses four main object types:

🔹 Blob (Binary Large Object)

  • Represents the contents of a file.
  • Git doesn’t care about filenames—just file contents.

Example:

echo "Hello Git" > hello.txt
git add hello.txt
git commit -m "Add hello.txt"

Inspect blob:

git hash-object hello.txt
git cat-file -p <blob_hash>

🔹 Tree

  • Represents a directory structure.
  • Stores filenames, permissions, and pointers to blobs/other trees.

Example:

git cat-file -p <tree_hash>

Output shows the file mode, type, hash, and filename.

🔹 Commit

  • A snapshot of the project at a point in time.
  • Stores:
    • Author & committer info
    • Commit message
    • Pointer to a tree object
    • Pointer(s) to parent commit(s)

Example:

git cat-file -p <commit_hash>

🔹 Tag

  • A named pointer to a commit.
  • Can be lightweight or annotated (with metadata, signatures).

Example:

git tag -a v1.0 -m "First release"
git show v1.0

4. How Git Builds History

Think of Git commits as nodes in a graph:

  • Each commit points to a tree (the project snapshot).
  • Each commit (except the first) has one or more parents.
  • This creates a directed acyclic graph (DAG) of history.

Visualize:

git log --oneline --graph --decorate

5. Refs and HEAD: Keeping Track of Where You Are

  • refs/ holds pointers to commits.
    • refs/heads/main → the latest commit on main.
    • refs/tags/v1.0 → a tagged commit.
  • HEAD points to the current branch or commit.
    • If you’re on main, HEAD points to refs/heads/main.
    • In detached HEAD state, it points directly to a commit.

Check it:

cat .git/HEAD

6. Exploring Git Internals Yourself

Some fun experiments:

  • See all objects in your repo: ls .git/objects
  • Dump commit data: git cat-file -p HEAD
  • Verify integrity of all objects: git fsck

7. Why This Matters

Understanding Git internals helps you:

  • Debug problems (e.g., lost commits, detached HEAD).
  • Appreciate why Git is fast and reliable.
  • Use advanced tools (reflog, filter-repo, bisect) with confidence.
  • Avoid fear when something goes wrong—you know how it works.

✅ Key Takeaways

  • Git stores everything as objects: blobs, trees, commits, tags.
  • Objects are identified by hashes (SHA-1/256).
  • Commits form a graph of history, not just a linear list.
  • .git contains the whole repository—you can reconstruct everything from it.
  • Knowing Git internals makes you a more confident and effective developer.

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