From mboxrd@z Thu Jan 1 00:00:00 1970 From: bqt@update.uu.se (Johnny Billquist) Date: Fri, 18 Mar 2016 03:13:29 +0100 Subject: [TUHS] Early non-Unix filesystems? In-Reply-To: References: Message-ID: <56EB6449.9010204@update.uu.se> On 2016-03-18 03:00, Warren Toomey wrote: > It's a bit off-topic, but what were non-Unix filesystems like around 1969-1970? > The PDP-7 filesystem has i-nodes (file metadata) and filenames separate > from the i-nodes. This allows hard links and thus a non-tree structured > filesystem. > > This has always struck me to be one of the most important features of > the Unix filesystem: names separated from the rest of the file metadata, > and arbitrary hard links so that there is no preferred filename. > > Were these features in other contemporaneous filesystems? I don't know exactly how contemporary ODS-1 is. It's the file system used on RSX-11, and I think it should atleast trace back to around 1972, but I can't say more for sure. Anyway, ODS-1, just like the Unix file system, have the directory hold just the filename and a file identifier (pretty much the same as inode number). There are of course some differences in details, but I would say it is very similar to how Unix works. ODS-1 do not have reference counting, but instead allows dangling directory entries that do not point to valid files. Instead ODS-1 have a generation counter for each file identifier, so that when it is reused, links to the old file will not accidentally refer to the new file. I would think that something like Multics had something similar, but I have no idea about that one... Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol