document direct mode files

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/internals.mdwn b/doc/internals.mdwn
index 34498b912..3136993f0 100644
--- a/doc/internals.mdwn
+++ b/doc/internals.mdwn
@@ -17,6 +17,15 @@ This two-level structure is used because it allows the write bit to be removed
 from the subdirectories as well as from the files. That prevents accidentially
 deleting or changing the file contents.
 
+In [[direct_mode]], file contents are not stored in here, and instead
+are stored directly in the file. However, the same symlinks are still
+committed to git, internally.
+
+Also in [[direct_mode]], some additional data is stored in these directories.
+`.cache` files contain cached file stats used in detecting when a file has
+changed, and `.map` files contain a list of file(s) in the work directory
+that contain the key.
+
 ## The git-annex branch
 
 This branch is managed by git-annex, with the contents listed below.