23 Apr
2026
23 Apr
'26
1:02 a.m.
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
23 Apr
23 Apr
3:36 a.m.
I have a PDP-10 KS10 with an RP06, RM03, and two TU45s. I also have a LCM MDE. I can test
your MDE-II, and have a ‘scope and logic analyzer for testing.
We have an 11/70 at the RICM that won’t get restored because there isn’t room to display a
pair of RM03s. An MDE-II would be helpful here.
We have an 11/40 running in the display area and could add an RH11 for Massbus device
testing.
On Apr 23, 2026, at 4:46 AM, Jim Bender via cctalk
<cctalk(a)classiccmp.org> wrote:
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
3:40 a.m.
What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS
devices? If you intend to emulate the interface, have you had a look at the
UNIBONE emulator? Using that one reduces the MASSBUS interface emulation to
a software problem only. And the community of UNIBONE users would be very
happy too if that emulation was added...
Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
2026, 10:46:
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
7 a.m.
I have a pdp 11/40 expansion chassis full of MASSBUS cards
b
On Thu, Apr 23, 2026 at 6:40 AM Hans-Ulrich Hölscher via cctalk <
cctalk(a)classiccmp.org> wrote:
What are you emulating - the UNIBUS MASSBUS interface
or the MASSBUS
devices? If you intend to emulate the interface, have you had a look at the
UNIBONE emulator? Using that one reduces the MASSBUS interface emulation to
a software problem only. And the community of UNIBONE users would be very
happy too if that emulation was added...
Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
2026, 10:46:
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
8:08 a.m.
Indeed. I still have a RM80 MASSBUS drive for MC (Decsystem/20) here,
and the thought of firing it up fills me with dread.
Running a "modern" SMD drive that plugs into the SMD-ish side of the
MASSBUS controller on an RM02/03/05/80 would be the simplest (it's SMD
with some signals inverted because DEC is stupid). Running something
that attaches to the RH11-C would be ok, but to be honest the Unibone
with 18 bit circuitry would be the win. That way it's just a slot on the
computer and your disk and tape problems are solved.
Chris
On 4/23/26 06:40, Hans-Ulrich Hölscher via cctalk wrote:
What are you emulating - the UNIBUS MASSBUS interface
or the MASSBUS
devices? If you intend to emulate the interface, have you had a look at the
UNIBONE emulator? Using that one reduces the MASSBUS interface emulation to
a software problem only. And the community of UNIBONE users would be very
happy too if that emulation was added...
Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
2026, 10:46:
> 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
>
>
8:37 a.m.
Yes, there are simpler ways to approach the disk/tape storage problem, and for
the most part it is already solved on 16 bit machines-- i.e., the unibus SCSI
card plus a ZuluSCSI if you want to get away from spinning media entirely or
perhaps a unibone.
For 18 bit disks the situation is a bit more complicated, which is likely one
of the reasons the original LCM Massbus emulator came into existence.
The goal of this project isn't just to "solve" the disk/tape problem, it is
also to be able to utilize a major hardware component of the systems that most
people have avoided in recent years because of the unwieldy, power-hungry and
relatively low capacity drives normally connected to it.
For some systems, Massbus is a better way to attach storage than on the
unibus, and on other systems the only really practical way.
On 4/23/2026 10:08 AM, Chris Zach via cctalk wrote:
Indeed. I still have a RM80 MASSBUS drive for MC
(Decsystem/20) here, and the
thought of firing it up fills me with dread.
Running a "modern" SMD drive that plugs into the SMD-ish side of the MASSBUS
controller on an RM02/03/05/80 would be the simplest (it's SMD with some
signals inverted because DEC is stupid). Running something that attaches to
the RH11-C would be ok, but to be honest the Unibone with 18 bit circuitry
would be the win. That way it's just a slot on the computer and your disk and
tape problems are solved.
Chris
On 4/23/26 06:40, Hans-Ulrich Hölscher via cctalk wrote:
> What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS
> devices? If you intend to emulate the interface, have you had a look at the
> UNIBONE emulator? Using that one reduces the MASSBUS interface emulation to
> a software problem only. And the community of UNIBONE users would be very
> happy too if that emulation was added...
>
> Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
> 2026, 10:46:
>
>> 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
>>
>>
12:10 p.m.
Jim:
Oh absolutely, and no shade meant on the problem. The Vax 8600/780/750,
the pdp11/70, and the DecSystem 2050/2060/2065all have dedicated Massbus
channels that don't deal with Unibus. So a device that plugs into the
end of a MBA cable would be neat without a doubt.
My 2020 is one little chunk of the puzzle, and I am planning to get a
pair of Unibones so I can emulate disks (somewhat important) and a TU77
tape drive (really important). Tape is the big issue, as only the TU45
and TU77 (maybe the TU16, I forget) are supported on a 2020 and both
require the extremely rare TM03 with the 18 bit fiddler (AI has one on
the TU77 there, but I don't think I want to ship my 20 out to Washington
to use it again :-)
An emulator that could do an RM80/RP06/RP07 would be quite handy. If you
need someone to test it, I'd be happy to assist.
CZ
On 4/23/26 11:37, Jim Bender via cctalk wrote:
Yes, there are simpler ways to approach the disk/tape storage problem,
and for
the most part it is already solved on 16 bit machines-- i.e., the
unibus SCSI
card plus a ZuluSCSI if you want to get away from spinning media
entirely or
perhaps a unibone.
For 18 bit disks the situation is a bit more complicated, which is
likely one
of the reasons the original LCM Massbus emulator came into existence.
The goal of this project isn't just to "solve" the disk/tape problem,
it is
also to be able to utilize a major hardware component of the systems
that most
people have avoided in recent years because of the unwieldy,
power-hungry and
relatively low capacity drives normally connected to it.
For some systems, Massbus is a better way to attach storage than on the
unibus, and on other systems the only really practical way.
On 4/23/2026 10:08 AM, Chris Zach via cctalk wrote:
> Indeed. I still have a RM80 MASSBUS drive for MC (Decsystem/20) here,
> and the thought of firing it up fills me with dread.
>
> Running a "modern" SMD drive that plugs into the SMD-ish side of the
> MASSBUS controller on an RM02/03/05/80 would be the simplest (it's
> SMD with some signals inverted because DEC is stupid). Running
> something that attaches to the RH11-C would be ok, but to be honest
> the Unibone with 18 bit circuitry would be the win. That way it's
> just a slot on the computer and your disk and tape problems are solved.
>
> Chris
>
> On 4/23/26 06:40, Hans-Ulrich Hölscher via cctalk wrote:
>> What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS
>> devices? If you intend to emulate the interface, have you had a look
>> at the
>> UNIBONE emulator? Using that one reduces the MASSBUS interface
>> emulation to
>> a software problem only. And the community of UNIBONE users would be
>> very
>> happy too if that emulation was added...
>>
>> Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
>> 2026, 10:46:
>>
>>> 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
>>>
>>>
4:36 p.m.
Why do we do these things? I'm working on porting a multitasking forth I
wrote in the 80's to a Mac plus rom replacement.
Jim.
On Thu, Apr 23, 2026 at 12:10 PM Chris Zach via cctalk <
cctalk(a)classiccmp.org> wrote:
Jim:
Oh absolutely, and no shade meant on the problem. The Vax 8600/780/750,
the pdp11/70, and the DecSystem 2050/2060/2065all have dedicated Massbus
channels that don't deal with Unibus. So a device that plugs into the
end of a MBA cable would be neat without a doubt.
My 2020 is one little chunk of the puzzle, and I am planning to get a
pair of Unibones so I can emulate disks (somewhat important) and a TU77
tape drive (really important). Tape is the big issue, as only the TU45
and TU77 (maybe the TU16, I forget) are supported on a 2020 and both
require the extremely rare TM03 with the 18 bit fiddler (AI has one on
the TU77 there, but I don't think I want to ship my 20 out to Washington
to use it again :-)
An emulator that could do an RM80/RP06/RP07 would be quite handy. If you
need someone to test it, I'd be happy to assist.
CZ
On 4/23/26 11:37, Jim Bender via cctalk wrote:
Yes, there are simpler ways to approach the disk/tape storage problem,
and for
the most part it is already solved on 16 bit machines-- i.e., the
unibus SCSI
card plus a ZuluSCSI if you want to get away from spinning media
entirely or
perhaps a unibone.
For 18 bit disks the situation is a bit more complicated, which is
likely one
of the reasons the original LCM Massbus emulator came into existence.
The goal of this project isn't just to "solve" the disk/tape problem,
it is
also to be able to utilize a major hardware component of the systems
that most
people have avoided in recent years because of the unwieldy,
power-hungry and
relatively low capacity drives normally connected to it.
For some systems, Massbus is a better way to attach storage than on the
unibus, and on other systems the only really practical way.
On 4/23/2026 10:08 AM, Chris Zach via cctalk wrote:
> Indeed. I still have a RM80 MASSBUS drive for MC (Decsystem/20) here,
> and the thought of firing it up fills me with dread.
>
> Running a "modern" SMD drive that plugs into the SMD-ish side of the
> MASSBUS controller on an RM02/03/05/80 would be the simplest (it's
> SMD with some signals inverted because DEC is stupid). Running
> something that attaches to the RH11-C would be ok, but to be honest
> the Unibone with 18 bit circuitry would be the win. That way it's
> just a slot on the computer and your disk and tape problems are solved.
>
> Chris
>
> On 4/23/26 06:40, Hans-Ulrich Hölscher via cctalk wrote:
>> What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS
>> devices? If you intend to emulate the interface, have you had a look
>> at the
>> UNIBONE emulator? Using that one reduces the MASSBUS interface
>> emulation to
>> a software problem only. And the community of UNIBONE users would be
>> very
>> happy too if that emulation was added...
>>
>> Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr.
>> 2026, 10:46:
>>
>>> 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
>>>
>>>
24 Apr
24 Apr
12:26 p.m.
New subject: Why do we do these things? (was: Massbus emulation)
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.
One of the things on my to-doom list is to play with it
and write up more applications than just listing a directory
and printing the contents of a file.
BLS
On Thu, Apr 23, 2026 at 04:36:23PM -0700, Jim Davis via cctalk wrote:
Why do we do these things? I'm working on porting
a multitasking forth I
wrote in the 80's to a Mac plus rom replacement.
Jim.
On Thu, Apr 23, 2026 at 12:10?PM Chris Zach via cctalk <
cctalk(a)classiccmp.org> wrote:
> Jim:
>
> Oh absolutely, and no shade meant on the problem. The Vax 8600/780/750,
> the pdp11/70, and the DecSystem 2050/2060/2065all have dedicated Massbus
> channels that don't deal with Unibus. So a device that plugs into the
> end of a MBA cable would be neat without a doubt.
>
> My 2020 is one little chunk of the puzzle, and I am planning to get a
> pair of Unibones so I can emulate disks (somewhat important) and a TU77
> tape drive (really important). Tape is the big issue, as only the TU45
> and TU77 (maybe the TU16, I forget) are supported on a 2020 and both
> require the extremely rare TM03 with the 18 bit fiddler (AI has one on
> the TU77 there, but I don't think I want to ship my 20 out to Washington
> to use it again :-)
>
> An emulator that could do an RM80/RP06/RP07 would be quite handy. If you
> need someone to test it, I'd be happy to assist.
>
> CZ
>
> On 4/23/26 11:37, Jim Bender via cctalk wrote:
> >
> > Yes, there are simpler ways to approach the disk/tape storage problem,
> > and for
> > the most part it is already solved on 16 bit machines-- i.e., the
> > unibus SCSI
> > card plus a ZuluSCSI if you want to get away from spinning media
> > entirely or
> > perhaps a unibone.
> >
> > For 18 bit disks the situation is a bit more complicated, which is
> > likely one
> > of the reasons the original LCM Massbus emulator came into existence.
> >
> > The goal of this project isn't just to "solve" the disk/tape
problem,
> > it is
> > also to be able to utilize a major hardware component of the systems
> > that most
> > people have avoided in recent years because of the unwieldy,
> > power-hungry and
> > relatively low capacity drives normally connected to it.
> >
> > For some systems, Massbus is a better way to attach storage than on the
> > unibus, and on other systems the only really practical way.
> >
> >
> >
> > On 4/23/2026 10:08 AM, Chris Zach via cctalk wrote:
> >> Indeed. I still have a RM80 MASSBUS drive for MC (Decsystem/20) here,
> >> and the thought of firing it up fills me with dread.
> >>
> >> Running a "modern" SMD drive that plugs into the SMD-ish side of
the
> >> MASSBUS controller on an RM02/03/05/80 would be the simplest (it's
> >> SMD with some signals inverted because DEC is stupid). Running
> >> something that attaches to the RH11-C would be ok, but to be honest
> >> the Unibone with 18 bit circuitry would be the win. That way it's
> >> just a slot on the computer and your disk and tape problems are solved.
> >>
> >> Chris
> >>
> >> On 4/23/26 06:40, Hans-Ulrich H?lscher via cctalk wrote:
> >>> What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS
> >>> devices? If you intend to emulate the interface, have you had a look
> >>> at the
> >>> UNIBONE emulator? Using that one reduces the MASSBUS interface
> >>> emulation to
> >>> a software problem only. And the community of UNIBONE users would be
> >>> very
> >>> happy too if that emulation was added...
> >>>
> >>> Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23.
Apr.
> >>> 2026, 10:46:
> >>>
> >>>> 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
> >>>>
> >>>>
>
12:34 p.m.
New subject: Why do we do these things? (was: Massbus emulation)
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
25 Apr
25 Apr
3:27 a.m.
On Fri, Apr 24, 2026 at 6:47 AM Jim Davis via cctalk
<cctalk(a)classiccmp.org> wrote:
Why do we do these things?
I guess for the same reason that I've spent the last few weeks
literally playing with 'toys'.
The toy in question is Fischertechnik, a rather nice construction
system for hackish engineering. Back in the mid-1980s they sold a set
to be controlled by a typical home computer. I have that set and the
interface to the BBC micro.
Turns out (after a bit of investigation) that adding a single wire to
the interface circuit board makes it compatible with the IBM PC
version of the interface, which connects to the parallel port on said
machine.
But that wasn't enough for me. No, I've now linked it to the parallel
port on my Osborne 1, written the driver software in Z80 assembly
language and ported most of the demonstration programs (BASIC, most of
the 'porting' was due to the differences in the screen display of the
IBM PC and the Osborne).
Why?
Because it's FUN!
-tony
23 Apr
23 Apr
11:48 p.m.
On 4/23/2026 2:10 PM, Chris Zach via cctalk wrote:
Jim:
I am planning to get a pair of Unibones
I need a couple of Unibones for myself and I am planning to do a run of the
boards with the surface mount components installed. You would need to source
the other parts, but that isn't too difficult (digikey, mouser, etc). I don't
really have the spare cycles to build complete boards for others, but if
someone was very persuasive, maybe...
If anybody wants one/some let me know and I can adjust the number of boards in
the run. Not sure at the moment how much the per-piece cost would be, but
last time I checked it wasn't bad... less than importing from Europe, anyway.
Jim
24 Apr
24 Apr
8:16 a.m.
Hi Jim:
I am also looking for a UniBone, to help me diagnose some core issues on my 11/05.
Please add me to your list of interested parties!
Kevin McQuiggin
mcquiggi(a)me.com
25 Apr
25 Apr
6:38 a.m.
FWIW, I have Joerg's qbone and unibone bare boards (listed at my
inventory page at https://wiki.bonedaddy.net/doku.php?id=boardinventory
down under the DEC boards section.)
They're unpopulated. They have "real" hard gold fingers. They were
purchased in bulk before all the tariff increases (so lower price than I
could get them for now in the US) and I do this for a hobby so sell at cost.
Please email me directly if interested.
Thanks,
Todd
On 4/24/2026 2:48 AM, Jim Bender via cctalk wrote:
>
>
> On 4/23/2026 2:10 PM, Chris Zach via cctalk wrote:
>> Jim:
>>
>> I am planning to get a pair of Unibones
>
> I need a couple of Unibones for myself and I am planning to do a run
> of the
> boards with the surface mount components installed. You would need to
> source
> the other parts, but that isn't too difficult (digikey, mouser, etc).
> I don't
> really have the spare cycles to build complete boards for others, but if
> someone was very persuasive, maybe...
>
> If anybody wants one/some let me know and I can adjust the number of
> boards in
> the run. Not sure at the moment how much the per-piece cost would
> be, but
> last time I checked it wasn't bad... less than importing from Europe,
> anyway.
>
> Jim
3:13 p.m.
I went off the rez, Here's the code if anyone is curious, Free as in beer.
https://github.com/jimmydevice/68K-multitasking-forth
On Sat, Apr 25, 2026 at 6:45 AM Todd Goodman via cctalk <
cctalk(a)classiccmp.org> wrote:
FWIW, I have Joerg's qbone and unibone bare boards
(listed at my
inventory page at https://wiki.bonedaddy.net/doku.php?id=boardinventory
down under the DEC boards section.)
They're unpopulated. They have "real" hard gold fingers. They were
purchased in bulk before all the tariff increases (so lower price than I
could get them for now in the US) and I do this for a hobby so sell at
cost.
Please email me directly if interested.
Thanks,
Todd
On 4/24/2026 2:48 AM, Jim Bender via cctalk wrote:
>
>
> On 4/23/2026 2:10 PM, Chris Zach via cctalk wrote:
>> Jim:
>>
>> I am planning to get a pair of Unibones
>
> I need a couple of Unibones for myself and I am planning to do a run
> of the
> boards with the surface mount components installed. You would need to
> source
> the other parts, but that isn't too difficult (digikey, mouser, etc).
> I don't
> really have the spare cycles to build complete boards for others, but if
> someone was very persuasive, maybe...
>
> If anybody wants one/some let me know and I can adjust the number of
> boards in
> the run. Not sure at the moment how much the per-piece cost would
> be, but
> last time I checked it wasn't bad... less than importing from Europe,
> anyway.
>
> Jim
26 Apr
26 Apr
7:52 a.m.
My apologies, I made a mistake and don't have Joerg's qbone boards, just
his qprobe.
I do have his Unibone bare boards.
I'd be happy to look into doing a run (and check on populating at least
surface mount chips) but it probably doesn't make sense given
Decromancer's qprobe dual.
Todd
On 4/25/2026 9:38 AM, Todd Goodman wrote:
>
> FWIW, I have Joerg's qbone and unibone bare boards (listed at my
> inventory page at
> https://wiki.bonedaddy.net/doku.php?id=boardinventory down under the
> DEC boards section.)
>
> They're unpopulated. They have "real" hard gold fingers. They were
> purchased in bulk before all the tariff increases (so lower price than
> I could get them for now in the US) and I do this for a hobby so sell
> at cost.
>
> Please email me directly if interested.
>
> Thanks,
>
> Todd
>
> On 4/24/2026 2:48 AM, Jim Bender via cctalk wrote:
>>
>>
>> On 4/23/2026 2:10 PM, Chris Zach via cctalk wrote:
>>> Jim:
>>>
>>> I am planning to get a pair of Unibones
>>
>> I need a couple of Unibones for myself and I am planning to do a run
>> of the
>> boards with the surface mount components installed. You would need
>> to source
>> the other parts, but that isn't too difficult (digikey, mouser,
>> etc). I don't
>> really have the spare cycles to build complete boards for others, but if
>> someone was very persuasive, maybe...
>>
>> If anybody wants one/some let me know and I can adjust the number of
>> boards in
>> the run. Not sure at the moment how much the per-piece cost would
>> be, but
>> last time I checked it wasn't bad... less than importing from Europe,
>> anyway.
>>
>> Jim
23 Apr
23 Apr
9:03 a.m.
On Thu, Apr 23, 2026 at 11:08 AM Chris Zach via cctalk
<cctalk(a)classiccmp.org> wrote:
Running a "modern" SMD drive that plugs into
the SMD-ish side of the
MASSBUS controller on an RM02/03/05/80 would be the simplest (it's SMD
with some signals inverted because DEC is stupid).
I worked for a guy in the late 80s and we tried to convert an RM03
drive back into a 9762 (he had Unibus SMD controllers and at the time,
RM02/RM03 drives were practically free). We never did figure out all
the changes, and we had a real 9762 right there to compare.
I have several systems with Systems Industries SMD adapters (that
largely go back to SI interfaces in system busses on their hosts).
I'd _love_ some real SMD drive emulators vs spinning up 45-year-old
rust.
-ethan
8:20 a.m.
Hello Hans:
It is an emulator of the Massbus devices. Connects directly to the unmodified
Massbus controller in a Massbus-capable system. Pretends to be things like
RM03, RM05, RP06, etc.
The idea is to not place any disks on the Unibus, although a RH11 would be
be able to talk to it and that is a Unibus device.
What you are describing sounds like adding an emulated RH11 to the Unibone.
Not out of the question, but a project for later down the road...
Thanks,
Jim
On 4/23/2026 5:40 AM, Hans-Ulrich Hölscher wrote:
What are you emulating - the UNIBUS MASSBUS interface
or the MASSBUS devices?
If you intend to emulate the interface, have you had a look at the UNIBONE
emulator? Using that one reduces the MASSBUS interface emulation to a software
problem only. And the community of UNIBONE users would be very happy too if
that emulation was added...
Jim Bender via cctalk <cctalk(a)classiccmp.org <mailto:cctalk@classiccmp.org>>
schrieb am Do., 23. Apr. 2026, 10:46:
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 <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
24 Apr
24 Apr
12:40 a.m.
Hi all,
A massbus emulation would be nice, but a real RM or CDC drive would be nice also.
Based on that I‘m interested in a massbus controller for Unibus (45, 55, 70).
Best
Andreas
Am 23.04.2026 um 17:21 schrieb Jim Bender via cctalk
<cctalk(a)classiccmp.org>rg>:
Hello Hans:
It is an emulator of the Massbus devices. Connects directly to the unmodified
Massbus controller in a Massbus-capable system. Pretends to be things like
RM03, RM05, RP06, etc.
The idea is to not place any disks on the Unibus, although a RH11 would be
be able to talk to it and that is a Unibus device.
What you are describing sounds like adding an emulated RH11 to the Unibone.
Not out of the question, but a project for later down the road...
Thanks,
Jim
> On 4/23/2026 5:40 AM, Hans-Ulrich Hölscher wrote:
> What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS devices? If you
intend to emulate the interface, have you had a look at the UNIBONE emulator? Using that
one reduces the MASSBUS interface emulation to a software problem only. And the community
of UNIBONE users would be very happy too if that emulation was added...
> Jim Bender via cctalk <cctalk(a)classiccmp.org
<mailto:cctalk@classiccmp.org>> schrieb am Do., 23. Apr. 2026, 10:46:
> 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 <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
23 Apr
23 Apr
7:03 a.m.
On Thu, Apr 23, 2026 at 4:46 AM Jim Bender via cctalk
<cctalk(a)classiccmp.org> wrote:
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?
I have a DR750 in the VAX-11/750 I saved from work 30 years ago - we
used it for a TU78 and we had non-MASSBUS storage (Unibus and a
Systems Industries 9400 on a CMI card that was next to the DR750). I
also have at least one 11/70 that could use MASSBUS devices.
Since Mesa 5I22 cards are now pretty much
unobtainium...
The result is a redesigned D/R board that
accepts a Terasic DE10-Nano directly.
I'm familiar with the DE10 series. I have a couple of DE10-Lite
boards for RL02 emulation. Excellent choice.
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.
I have System Adminstrator-level experience with MASSBUS from the
1980s (connecting and using but not repairing), and no experience with
the LCM project. I can offer encouragement though, and in the far
future, I can offer up a possible test example in the way of an 11/750
with DR750 (it would need to be cleaned and tested first - hasn't been
powered on in many years due to a lack of a 30A socket where it's at).
I would also be happy to avoid the MASSBUS cabling issue by connecting
an emulator right to the 11/750 backplane with short or medium length
40-pin cables (the usual arrangement is short flat cables that go from
the backplane to a standard MASSBUS ZIF connector on the I/O buikhead,
then a fat round cable to the first device). I have at least one
original round MASSBUS cable but if there's no reason to pile it up
behind the machine, so much the better.
I guess that also depends on one's physical arrangement, if it's going
to be CPU + Emulator only or CPU + emulator + real MASSBUS devices
further down the chain.
In my case, I'd only ever have that 11/750 or an 11/70 to worry about,
but this device would also be great for someone with a KS10.
-ethan
4:26 p.m.
Jim Bender via cctalk <cctalk(a)classiccmp.org> writes:
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.
[ snip ]
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.
You rang?
I forwarded Jim's message to the two guys who did the original and
follow-on Massbus Disk Emulators, and one of them has already responded
to him directly.
The history, for those who are interested:
In 2004, we restored a DECSYSTEM-2065 which Len Bosack of XKL sold to
Paul Allen in 2000-2001, as part of getting several systems running in
PGA's personal collection. We also restored a pair of RP06 disk drives,
including purchasing the last NOS HEPA filters for them, but it was very
hard to find new media.
My colleague Keith Perez, a wizard at this kind of thing, suggested that
he could build an emulator for the disk drives in short order, and spent
the next two years creating the original MDE. This was based on a
Rabbit processor accompanied by about half a dozen PIC processors; the
back end was a Slackware Linux system which served up files representing
individual tracks via FTP. (I wrote my first ever C code in anger
making the Rabbit's FTP program actually work.)
This was fast enough to emulate 4 RP06 drives and allowed us to run
Tops-10 v7.04 on the 2065, which we opened for public access accounts
under the PDPplanet.com umbrella.
In December 2011, I arranged for the museum to acquire a KI-10 from a
collector in Germany; PGA insisted that we get it running before the end
of 2012. By that time, Bruce Sherry was working for the museum, and
proposed that he refrangle the design using an FPGA in place of Keith's
board full of Rabbit and PICs; his version was fast enough to supply a
full 8 RP07 drives, so we used 2 on the KL-10 system to give it the RP06
it needed for booting the 11/40 front end. The KI-10 used one since it
booted directly from the PDP-10 formatted disk.
Early on, Michael Thompson was very helpful to Keith in getting the
original design working, in exchange for the promise of an MDE when it
was working. We were finally able to fulfill that promise with one of
Bruce's units.
In addition to running the KL-10 and KI-10 systems (Tops-10 v7.04 and
v6.03A, respectively), we ran the former MIT-AI KS-10 system under ITS
using one of Bruce's units.
--
Rich Alderson news(a)alderson.users.panix.com
Audendum est, et veritas investiganda; quam etiamsi non assequamur,
omnino tamen proprius, quam nunc sumus, ad eam perveniemus.
--Galen
24 Apr
24 Apr
1:54 a.m.
Rich Alderson wrote:
we ran the former MIT-AI KS-10 system under ITS using
one of Bruce's
units.
Can confirm. I provided a new purpose-built disk image made with a
PDP-10 emulator. It was good to be able to verify it running on real
hardware, including the freshly reassembled microcode.
7:46 a.m.
I have a couple of 11/70's here that I'd love to have use their abandoned
RH11 board sets. I'm somewhat desperately hanging disk off UNIBUS (via
Emulex) at the moment and have heard anecdotes about how pathetic that
throughput is compared to MASSBUS. So I'd definitely be in as a testing
resource and hopefully for acquiring a unit once completed.
It's funny, I was just asking whether there's current MASSBUS device
emulation happening a few months back when first I acquired these machines,
before building them, and suddenly boom, my wishes are coming true :-)
Thank you all!
jake
On Fri, Apr 24, 2026, 6:39 AM Lars Brinkhoff via cctalk <
cctalk(a)classiccmp.org> wrote:
Rich Alderson wrote:
we ran the former MIT-AI KS-10 system under ITS
using one of Bruce's
units.
Can confirm. I provided a new purpose-built disk image made with a
PDP-10 emulator. It was good to be able to verify it running on real
hardware, including the freshly reassembled microcode.
8
days inactive
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22 comments
16 participants
participants (16)
-
Bill Degnan -
Brian L. Stuart -
Chris Zach -
Ethan Dicks -
Hans-Ulrich Hölscher -
hupfadekroua -
Jacob Ritorto -
Jim Bender -
Jim Davis -
Lars Brinkhoff -
mcquiggi＠sfu.ca -
Michael Thompson -
Paul Koning -
Rich Alderson -
Todd Goodman -
Tony Duell