How does git detect that a file has been modified?

Question

How does git detect a file modification so fast?

Does it hash every file in the repo and compare SHA1s? This would take a lot of time, wouldn\'t it?

Or does

Answer 1

Depending on platform, you should be able to find out what syscalls Git uses to figure out its status. Try strace git status on Linux, truss git status on SunOS, or the seemingly DTrace-based tool that Apple ships with its Developer Tools on Mac OS X.