[TUHS] Early non-Unix filesystems?

Johnny Billquist bqt at update.uu.se
Fri Mar 18 12:13:29 AEST 2016

On 2016-03-18 03:00, Warren Toomey <wkt at tuhs.org> 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 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

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