Some PDP-11 info (was Re: C compilers for RSTS/E?)

From: Ed Kelleher <>
Date: Sat Oct 23 05:10:42 2004

At 11:12 PM 10/22/2004, Graham wrote:

>I think RT-11 had version numbers (in the style of VMS), but GUTS
>showed only the top-level file, and had a "pop" command which deleted
>the most recent file and made the version below it visible.
>The source is lost (though we do have a disk pack which *may* contain
>the OS, if it is still readable) but a scan of the three-book report
>is available online: -
>Orange is the users guide; Red - system design; Yellow - selected
>source listings.
>Another PDP/11 O/S was "MUSS". There's a manual page for it
>I think the sources of MUSS along with the FEP's and ERTE are in
>that directory somewhere too. DEIMOS, MUSS, ERTE and the FEPs
>were written by Brian Gilmore, now head of the Computing Service.
>Ian Young wrote an operating system for the PDP-11 called "rats"
>as a student project - I believe he has a paper listing which we
>might have scanned some day. That was the first implementation
>of lightweight threads that I remember seeing.
>All the Edinburgh software was written in Imp, except for a few
>assembler parts, but we had our own assembler for it as well:
>There were two compilers for the system; one written by the ERCC
>based on a simpler bootstrapping compiler called "SKIMP" -

Though my wife likes RT11,
I think she would draw the line at a MUSS of Red, Orange and Yellow lmp
rats GUTS.

RT11 file structure didn't have version numbers.
Didn't even keep time of creation, just a single date.
No attributes either, except RO in later versions.
Just 1 directory for entire disk.
There were a few words available in each directory file entry for user
Big thing: files had to be contiguous.
As files were deleted they made free spaces.
New files could only be as large as the largest free space on a disk.
Had to compress (squeeze) the file structure periodically to consolidate
all the free spaces.

My wife, before we were married, used that to set the hook in me.

She was a Dibol programmer who had graduated from programming on a PDP 8/A
to a PDP 11/34.
I was the geek upstairs building M6800 tape readers and programming them
with the ASR33.

No command language in those days, RT11 V2c was strictly command line.
Dibol compiler had a /S switch to suppress data division summary in source
PIP /S was used to squeeze the disk.

Dibol would let you use ^C to stop the program and source listing.
That was accepted practice.
PIP would let you use ^C to abort it in the middle of rewriting your disk
That was definitely NOT good practice.

Girl comes crying into room, "I did PIP/S and not DICOMP/S and ^C'd and
I've lost all my work!!!".
(Don't you just love it when they talk like that!)
Geek boy helps pretty programmer recover data, gets big kiss, etc. etc.

Yup, RT11 was definitely useful despite it's limitations.
I doubt she'd have hung around long enough for us to meet if she'd had to
work on a MUSS of lmp rats GUTS.


Ed K.
Received on Sat Oct 23 2004 - 05:10:42 BST

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