The Commit Graph

Git is, at heart, a graph of commits. Each commit is a snapshot of your project plus a pointer to its parent — the commit that came before it. Follow the parents back and you have the full history. Because commits only ever point backward, the structure is a directed acyclic graph (DAG).

Run some commands and watch the graph grow. commit adds a node; new branch starts a parallel line of work; merge ties two lines back together.

Branches are pointers

A branch is not a copy of your files — it’s just a lightweight, movable pointer to a commit. When you git commit, Git creates the new commit and slides the current branch pointer forward to it. That’s why branching is cheap: making one is just writing down a commit id.

HEAD: where you are

HEAD points to the branch you currently have checked out (here, HEAD → main). Commits attach to wherever HEAD is. git checkout <branch> just moves HEAD to a different pointer — your next commit then extends that line.

Why a DAG

Every commit records its parent(s), so history is a graph, not a straight line. Branches let two lines of work proceed independently from a shared ancestor; a merge (next lesson) joins them with a commit that has two parents. Nothing ever points forward, so there are no cycles — it’s always a DAG.

Takeaways

• A commit is a snapshot plus a link to its parent; the history is a DAG.
• A branch is just a movable pointer to a commit — cheap to create.
• HEAD marks your current branch; commits extend wherever HEAD points.