Starring the PDP11/20 with Unibone

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Jul 18, 2022, 11:29:29 AM7/18/22
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Hello all,

Okay, don't take this one too serious please  I've put my PDP11/20 on YouTube for a demo. One can show programmers stuff, I thought I do something different. I hope you like it. And don't mention the way I close the lower RK05 at the end 🤔 This is not like DEC explains it in the manual...😇

I did a topic about restoring the RK05 drives

And A story about the PDP11/20

I didn't do a story on the TC11 and TU56H unfortunately. But it came don to a few broken TTL chips, two burned motor driver boards, bad capacitors in the H720 power, and the two motor capacitors were bad as well...

I still have to fix my 4KW core memory module, but at least it is complete.

But the Unibone was very helpful in the process to restore the PDP11/20 and peripherals. And it is still very helpful to fill up the memory to the max for this machine and emulate RL drives. So that is why I post it here too...

Regards, Roland

Joerg Hoppe

Jul 19, 2022, 3:21:33 PM7/19/22
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Hi Roland,
great and fulfilling work!
I envy you for a running '20, ours is still quite scrappy.

And your youtube video clearly shows: you sucessfully compelted the flow chart at

kind regards,

Ethan Dicks

Jul 19, 2022, 6:15:52 PM7/19/22
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On Tue, Jul 19, 2022 at 3:21 PM Joerg Hoppe <> wrote:
> Hi Roland,
> great and fulfilling work!
> I envy you for a running '20, ours is still quite scrappy.

Indeed. I am targeting my 11/20 for a Unibone but I have a lot of
work to do first (it was chopped up by my old supervisor and chucked
in the skip. A buddy of mine and I fished out the parts - I saved
90-95% of it).

At least I have several MM11 memory units (but not the PSUs - that's
one of the items that was kept when it was first scrapped). I will
probably get it working with either MOS memory or emulated memory
first before tackling the core.

One of my long-term restoration goals is to get RF11 emulation working
on the Unibone so I can run 1972 UNIX on it. I probably also need to
emulate a serial mux that UNIX knows about (DC11?) At least I have
the parts for the required KE11-A.

Very happy to see a working 11/20. Inspiring.

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