First, if it isn’t yet clear, Git is fundamentally a content-addressable filesystem with a VCS user interface written on top of it.
“plumbing” commands → 底层命令 ，“porcelain” commands → 上层命令
At the core of Git is a simple key-value data store.
Git Objects
dir is .git/objects
- Blob → file
- Tree → dir
commit object save who saved the snapshots, when they were saved, or why were saved. commit information and one tree snapshot.