COS-300 and DMS-500

From: Jack Peacock <>
Date: Wed Jan 8 19:29:00 2003

> Speaking of DIBOL, I need COS-300 for some of my 11/23s... In case you
> didn't know, COS-300 is RT-11 with DIBOL layered on it or something..
> COS-500 is the same but its RSTS-based if I remember correctly..
What makes COS-300 hard to find is that most distributions were on RK05s,
DEC's low end 2.5MB front load cartridge hard drive. These were not the
most durable of drives and often succumbed to head crashes. However, it was
relatively easy to replace the heads, about an hour's work for field

COS-300 (Commercial Operating System 300) was an OEM package VARs sold to
small businesses in the 70's. A typical system was a smaller PDP, an 11/34
or 11/03, RT-11, and the DIBOL compiler, along with something added by the
VAR. There were several basic financial packages for the systems,
GL/AP/AR/PY or accountant client write-up being typical markets. Your
humble author developed some vertical apps for casinos and gas station
accounting on a 11/34 COS-300 system. 25 years later I'm still supporting
some of that legacy DIBOL code, now migrated to VMS and Alphas. Old
business apps never die, they just migrate to the next box...

COS-500 was for larger customers, who typically ran RSTS on 10 or more
terminals. BASIC was more common on these systems, which could range up to
a PDP-11/70.

I seem to recall there once was some sort of 5.25" floppy distribution in
the early 80's. It had RT-11 v4 and was primarily for 11/23 and 11/73
systems. This was for the odd dual floppy came out with, where two drives
shared one spindle and the top floppy was upside down. These were single
sided (400KB?) and used FILES-11 for the file system.

DMS-500 was DECs answer to the PICK operating system. PICK had made
substantial inroads in the medical field, especially hospitals, so DEC came
up with the same "put everything in the database" concept. Real CODASYL
databases were too big for PDP-11s so DMS-500 was the low end answer if you
couldn't afford a PDP-10 or PDP-20. As I understand PICK eventually
migrated to the IBM RS/6000 but DMS never got much support from DEC sales.
I think there was some version for VMS but it wasn't a major player on the
VAX compared to DBMS-32 and later Rdb and Oracle.
   Jack Peacock
Received on Wed Jan 08 2003 - 19:29:00 GMT

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