Open a real `.git/objects/` store, tell a blob, tree, and commit apart by what each holds, and predict why two identical files collapse to one hash.

You saved the folder three times: `notes/`, `notes-backup/`, `notes-final/`, and felt every copy waste space. Git quietly keeps every version too, yet `.git/objects/` barely grows and never once records 'what changed' between them.

Read the one line inside a branch file and the ref: line inside `.git/HEAD`, then predict which single file a commit changes versus a switch, and why detached HEAD is a shape rather than a break.

You run `git switch dev` and every file in your project changes at once, yet not a single saved commit has moved. Something tiny on disk got rewritten, and finding it explains why branching costs almost nothing.

Follow the hash each commit stores for the one before it to trace the whole graph, then slide a ref off a commit and watch the object survive on disk, reachable through the reflog until garbage collection's grace period lapses.

You made five commits building `config.json`, then one `git reset` seemed to delete the last one. Nothing was erased: every commit still sits on disk, and finding the pointer that orders them explains exactly where it went.