[Simh] RT-11 source

[Bob Eager]

On Sun, 23 Oct 2016 14:07:33 -0400
Paul Koning <paulkoning at comcast.net> wrote:

> I've never seen DOS sources.  Also, DOS/Batch is a later version with
> more stuff in it.  DOS V4 might be better.

I couldn't agree more. We had DOS/BATCH on an 11/20 in about 1974 (we'd
had it for a year or two before I got my hands one it). 

I know someone had to patch it as it used 12 bits for the date:

  date = (year-1970)*1000 + day in month

They called it a Julian date (which it wasn't, and of course it was
incredibly bit-wasteful). It 'ran out' in March 1974, and the patch was
regularly applied to fix dates so that we worked in the middle of a
four year window.

We also put it on RK05s, and I remember reading the (badly xeroxed)
sources that DEC gave us, and working out how to patch it to fix a
fairly nasty bug in the RK05 driver.

But it was amazingly small - 4kB resident, with hundreds of tiny
overlays. I think running a program used four 128kB overlays.

> On the other hand, DOS is a truly evil operating system.  I don't
> know its internals, but just from using it you can tell it should
> never be used as a model.

Indeed! I did fire it up on SIMH a while ago.

> RT-11 is very clean.  I've worked with V2A (the FB version when
> possible, SJ when I didn't have enough memory).  They are very simple
> and compact; the UI is the old TOPS-10 style, not the newer bloated
> "DCL" interface.  So a V2 era edition would be a good way to go.

Yes, it's very nice. Someone once gave me electronic copies of some
sources (circa 1975) and I read them with glee. Lovely comments, too:
the system call dispatcher had the comment "What's it going to be then,
eh?" from the Clockwork Orange. I think those comments were only in the
FB monitor.

I assembled it on DOS/BATCH, and wrote programs in MACRO-11 to convert
the binaries to RT-11 format. I also wrote stuff to make a bootable
DECtape, got it running, and used that to transfer it to disk!