> our commits document the diff, not the materialized snapshot That's not actually true, though. This is what a raw commit object looks like: $ git cat-file

> our commits document the diff, not the materialized snapshot That's not actually true, though. This is what a raw commit object looks like: $ git cat-file commit bfc766d38e1fae5767d43845c15c79ac8fa6d6af tree 99768f8965d5382d1c1695c371a854d061f2548b parent 860a3b34854d8abe9af9f1eb584691de926ce897 author Peter Maydell <peter.maydell@linaro.org> 1462981466 +0100 committer Peter Maydell <peter.maydell@linaro.org> 1462981466 +0100 Update version for v2.6.0 release Signed-off-by: Peter Maydell <peter.maydell@linaro.org> (This commit is from the QEMU project repository.) Note that there is no reference to a diff. There is a reference to a tree, which is a binary object representing a directory structure—a full snapshot of the state of the working tree as of that commit: $ git ls-tree 99768f8965d5382d1c1695c371a854d061f2548b 100644 blob 3ac0cfc6f0d60a95a5c3557497835c80e52a1696 .dir-locals.el 100644 blob 37755ede83a0d5b4fe22114f624a140d2bcaefff .exrc 100644 blob 88a80ff4a5c552bad3bc2bf40b1fc4a45c57a177 .gitignore 100644 blob 9da9ede26161bc5c6f12552b55bc54f55bb1e839 .gitmodules … Each of those blobs is a reference to the full content of the corresponding file: $ git cat-file blob 3ac0cfc6f0d60a95a5c3557497835c80e52a1696 # .dir-locals.el ((c-mode . ((c-file-style . "stroustrup") (indent-tabs-mode . nil)))) For storage purposes there is deduplication, delta encoding, and compression going on behind the scenes, so committing a 100M working tree with a few small changes doesn't take up 100M of additional storage space, but these are invisible to the upper layer. When Git needs a diff, for example to perform a three-way merge, or in response to `git show` command, it generates one on the fly from the snapshots.