That's what it looked like, but I doubt it was deep in the filesystem. It was basically just a naming convention. User had to purge old versions manually. This gets tedious if you have many files that change often. Snapshots are a safety net, not something you want to have in your way all day long.
Er.. my memory is that it did COW inside VMS fs semantics and was not manually achived. You did have to manually delete. So I don't think it was just a hack.
It didn't do directories so was certainly not as good as snapshot but we're talking 40 years ago!
>> DEC attempted to replace it with a log-structured file system file system named Spiralog first released in 1995. However, Spiralog was discontinued due to a variety of problems, including issues with handling full volumes.
Every file has a version number, which defaults to 1 if no other versions of the same filename are present (otherwise one higher than the greatest version). Every time a file is saved, rather than overwriting the existing version, a new file with the same name but an incremented version number is created. Old versions can be deleted explicitly, with the DELETE or the PURGE command, or optionally, older versions of a file can be deleted automatically when the file's version limit is reached (set by SET FILE/VERSION_LIMIT). Old versions are thus not overwritten, but are kept on disk and may be retrieved at any time. The architectural limit on version numbers is 32767. The versioning behavior is easily overridden if it is unwanted. In particular, files which are directly updated, such as databases, do not create new versions unless explicitly programmed.
