I think that the first thing to understand about Git is that it’s not strictly a source control system; it’s more like a versioned filesystem that happens to be good at source control. Traditionally, source control systems focused on the evolution of files. For example, RCS (and its successor CVS) maintain a separate file in the repository for each source file. These repository files hold the entire history of the file as a sequence of diffs that allow the tool to reconstruct any version. Subversion applies the idea of diffs to the entire repository, allowing it to track files as they move between directories.
Git takes a different approach. Rather than constructing the state of the repository via diffs, it maintains snapshots of the repository and constructs diffs from those (if you don’t believe this, read on).
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