[TUHS] Work I've done with a PDP-11 simulator

Norman Wilson norman at oclsc.org
Mon May 12 09:13:29 AEST 2014

  The web page mentions files-11 which is ODS-1.

Technically (it is all coming back to me now):

FILES-11 is a family of file systems that started in RSX-11
(or perhaps before but that's the oldest instance I know).

ODS-1 is really FILES-11 ODS-1; ODS is `on-disk [something].'

RSX-11 used ODS-1.  VMS used ODS-2.  I'm not sure of all
the differences offhand, but they were substantial enough
that we ended up writing two different programs to fetch
files to UNIX from RSX and VMS volumes (we had the latter
to deal with too).  Certainly the directory entries were
different between the two: ODS-1 used RADIX-50-encoded
file names with at most six characters plus an at-most-three-
character `extension' (a term which newbies sometimes
improperly import into UNIX as well); I forget the exact
filename rules in VMS, but filenames certainly could be
longer than six characters.

I've found the early-1980s programs I remembered.  There
were two, getrsx.c and getvms.c; two programs, one for
each file-system format.  They are surely full of ancient
sloppiness that won't compile or won't work right under
a modern C compiler, and they make assumptions about byte
order.  I'll spend some time in the next few days going over
them and see if I can quickly get something workable.

A footnote as to their origin: in the world where we wrote
these programs, we had not only multiple systems, but
shared disk drives.  The disk drives themselves were
dual-ported; the controllers we used could connect to
multiple hosts as well.  Each system had its own dedicated
disk drives, but the UNIX systems could also see the drives
belonging to the RSX and VMS systems; hence the file-fetching
programs, since this was well before the sort of networking
we take for granted these days.

On the other hand, we had several UNIX systems which spoke
uucp to one another, and that was occasionally used for
large file transfers.  To speed that up, I taught uucico
a new protocol, whereby control information still went over
a serial line, but data blocks were transferred over a
chunk of raw shared disk (with appropriate locks, of course).

It was a simpler world back then, but that made it a lot more fun.

Norman Wilson
Toronto ON

More information about the TUHS mailing list