Does anybody here still use Massbus?
Or have a Massbus system you’d like to run, but the idea of dealing with
washing-machine disk drives is a bit less appealing these days?
In what may classified as a momentary lapse of reason, I have taken up the old
Living Computer Museum Massbus emulator project and am in the process of
resurrecting / modernizing it.
Current progress photo here:
http://www.dmv.net/mbe/mbe1.jpg
Why, you ask? "Has he gone insane?" are you thinking?
I have three PDP-11/70s that I would like to get running again. Sure, I could
cheat and hang a UNIBUS SCSI controller with a ZuluSCSI disk simulator, but
where is the fun in that? Also, the 11/70 was designed and optimized around
Massbus for primary storage, so it seems only fitting to use it that way.
The original LCM emulator used a PC with a Mesa 5I22 FPGA card as the Massbus
interface. The FPGA implemented the drive-side bus logic, while the PC
software emulated the backing disk or tape image. A driver/receiver (“D/R”)
board sat in the middle to translate the Massbus differential signals into
logic levels suitable for the FPGA. It worked...
Since Mesa 5I22 cards are now pretty much unobtainium, I went looking for a
cleaner and more modern approach. The result is a redesigned D/R board that
accepts a Terasic DE10-Nano directly. The DE10-Nano is a small Linux SBC with
a Cyclone V FPGA onboard, so it can host the emulator software itself while
the FPGA handles the Massbus interface duties that were previously done by the
Xilinx FPGA on the Mesa card. Same general architecture, but much tidier.
There is still work to do, but it is coming along nicely. The board in the
photo is not yet fully populated, since I am doing incremental testing before
committing the rest of the parts.
As I have gone down this rabbit hole, naturally a few questions in the “why
did they do THAT??” category have come up...
paging @Rich Alderson ...
If anyone here is still actively using Massbus, has experience with the
original LCM project, or just has relevant war stories, comments, warnings, or
encouragement, I would be glad to hear them.
Cheers!
Jim
VCF West 2026 will be held on August 1st and 2nd at the Computer History
Museum in Mountain View, CA.
We have opened registration for exhibits, vendors, speakers, and volunteers.
Please visit our event application at
https://em.vcfed.org/events/vcf-west-2026 to register. Also, please note
that this software is new, so there may be a bug or two. Please report any
issues, or send any questions or comments to vcfwest(a)vcfed.org.
Thank you!
Jeff Brace
VCF West co-showrunner
It is nice to get back to these old programs.
A few years ago I fixed a bug in an undergrad chess “knight’s tour” program I wrote when I was about 18. It was written in PL/I.
Last edit: 1978; I happily added “bug fix, 2016”.
I knew of the bug, just never got around to fixing it. I added some printout improvements too.
I had the Hercules S/360 emulator running. MVS 3.7j I recall. Memory lane trip for sure. JCL? Had to find my “green book”!
Kevin
Sent from my iPhone
> On Apr 24, 2026, at 12:34, Paul Koning via cctalk <cctalk(a)classiccmp.org> wrote:
>
>
>
>> On Apr 24, 2026, at 3:26 PM, Brian L. Stuart via cctalk <cctalk(a)classiccmp.org> wrote:
>>
>> Very cool. A while back, I resurrected one of my senior
>> projects from 1984, a little Forth-based OS for the PDP-11.
>> It was originally implemented on an 11/34 with an RK05,
>> but now I've got it on a little LSI-11 in a BA11-VA box
>> with a little 6809 board I build and wrote a TU58 emulator
>> for.
>
> I recently started playing a lot more with Forth. The main reason is that I ran into a very nice extended Forth system for the Raspberry Pico, which makes for a much nicer development environment than the vendor-supplied C API. It's a bare metal system, implemented mostly in Forth with the low level bits in assembly language. No C or C++ anywhere.
>
> https://github.com/tabemann/zeptoforth
>
> It does networking, too. I've been using it to develop a nice NTP server (and disciplined oscillator), very nice and small.
>
> paul
>
At LSSM, we have 2 KS10s and 1 11/70. We have one of the LCM emulators
connected to a KS10, but alas, both KS10 power supplies are now deceased,
so we are working on replacements.
The emulator seems to work fine, for as much as we've used it.
Of course, the Massbus connectors are made of unobtanium and must be
scrounged from elsewhere.
Hello Sir,
I have this printer with Parallel Centronics connection.
How do I print something using modern pc?
Thanks for information on power connection, great help.
Thanks
Sunil
Dear Noel,
Thank you very much for making the M9301-YA.mac file publicly available (https://www.classiccmp.org/pipermail/cctalk/2015-April/006241.html), but I can't download it...
When I try to download it, I get the message: "You don't have permission to access /~jnc/tech/pdp11/M9301-YA.mac on this server."
Could you please email me the M9301-YA.mac file archive?
With best wishes
Roman
