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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 4th Aug 2022, 10:51 pm   #1
Roland Huisman
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Talking PDP11/20 demo

While being active here with my Mullard E7600/4 I saw the old computer section again. Recently I posted a demo on YouTube showing my PDP11/20 and also a demo of my Holborn 6500. I have no idea if this is of any interest here... I guess a few people from here are also active on vcfed.org... But it doesn't hurt to show it here as well I think.

Don't take this one too serious please 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...

The PDP11/20 was quite a tour getting it online again.
https://youtu.be/we548QRp7S4

I did a topic about restoring the RK05 drives
https://forum.vcfed.org/index.php?th...ersions.78961/

And A story about the PDP11/20
https://forum.vcfed.org/index.php?th...storing.80723/

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.

I made the demo of the Holborn 6500 back in 2014 and I though it was horrible when I watched it again. But I never made a new video so I posted it anyway.

https://youtu.be/pOyU_qNV30A

Recently I tested the machine again, but I have to replace some foam pads in the Keytronic keyboard. Oh well, these old beasts will keep you busy...

Regards, Roland
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Old 5th Aug 2022, 6:19 am   #2
Mark1960
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Default Re: PDP11/20 demo

I like the old PDP11 series, reminds me of all the time spent in the computer lab at university when I was supposed to be studying. They had PDP11/34 or 35 and later upgraded to 11/70 or 75 and were quite relaxed about system security prior to the upgrade. I don’t remember which type of RK05 it used. It also had a pair of 8 inch floppy drives which I think were a non standard addition. We had read write and execute access to the floppy drives so we could copy a shell program to the floppy and edit the file system to change the permissions to set user id to 0. Occasionally we would crash the system in the evenings and that would be end of play for the day.
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Old 7th Aug 2022, 4:23 pm   #3
Roland Huisman
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Default Re: PDP11/20 demo

Hi Mark,

Nice! The floppy was probably a RX01 / RX02 or an after market DSD440. In the 11/20 I have also the RX01 floppy controller, but the RX01 drive which I have is an external one. And I'm happy with that because it does not fit into the cabinet any more... But since these drives are from a later date then this PDP11 I thought lets keep de video simple with the devices from that time.

I always wondered how many machines were build in Galway since I have a few, but not all European machines were made in Galway.

Regards, Roland
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Old 7th Aug 2022, 4:38 pm   #4
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Default Re: PDP11/20 demo

Don't forget the Systime models, which were quite important in the UK minicomputer market for a while. The Systime PDPs weren't simply badged DEC models but were locally manufactured, sometimes down to component level. They fell out with DEC over US export controls to Eastern Europe in the mid 80s, and were history by the 90s.

https://en.wikipedia.org/wiki/Systime_Computers
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Old 7th Aug 2022, 5:08 pm   #5
Roland Huisman
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Default Re: PDP11/20 demo

Thanks for mentioning Systime! I've never heard about that brand. I will see if I can find any info about these machines.

Regards, Roland
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Old 7th Aug 2022, 5:31 pm   #6
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Default Re: PDP11/20 demo

Fascinating history here; in my early-80s IT stuff I had clients with the likes of PDP11/70, but rather more involvement with 'instrumentation' computers - we had a bunch of DEC MINC-11 [Modular INstrumentation Computer] systems - which were basically a PDP11/03 or the LSI-11 version, fitted into a sort of superranuated-oscilloscope-trolley. Twin floppy-drives, or - if you got lucky - a hard-drive. They ran RT-11 or [luxury!!] RSX11-M. Compiling a FORTRAN program involved lots of floppy-swaps.


We also had a few hundred LSI11/23 based controllers for CAMAC crates; these were really fun bits of simply-programmable gear which could be used for anything from controlling a nuclear-reactor to running a HASP workstation to log-in to an IBM/Amdahl/Honeywell mainframe and receive the output of your overnight batch-job.

CATHY and CATEX were the programming-labguages for these; I worked with Dave Hughes who was the designer of CATEX. [CATEX stood for CATHy-Extended].

"DL Protocol" - as invented by Daresbury Labs - was the big thing back then - I was DL.465.0

Thinking about Systime, there was also a 1980s company called "Fungus" who were big in the DEC market; I bought a bunch of controllers from them that let me hook up a string of Control-Data 300MB hard-drives to an 11/70.

More information on the MINC-11 here: https://fjkraan.home.xs4all.nl/comp/minc/index.html
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Last edited by G6Tanuki; 7th Aug 2022 at 5:48 pm.
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Old 7th Aug 2022, 6:44 pm   #7
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Default Re: PDP11/20 demo

Wow, nice.!
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Old 7th Aug 2022, 7:48 pm   #8
Mark1960
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Default Re: PDP11/20 demo

Quote:
Originally Posted by Roland Huisman View Post
Nice! The floppy was probably a RX01 / RX02 or an after market DSD440. In the 11/20 I have also the RX01 floppy controller, but the RX01 drive which I have is an external one. And I'm happy with that because it does not fit into the cabinet any more... But since these drives are from a later date then this PDP11 I thought lets keep de video simple with the devices from that time.
Hi Roland, Iím not sure what the model of the floppy drive was, just that it was a seperate dual single sided 8 inch drive unit in the same room as the user terminals while the main unit rack was in the adjacent room. This was 1978 onwards if that helps identify the possible model.

There was another machine in the system room with a vector graphic display. It might have been a PDP10. We would sometimes get to play moon lander on it, the objective was to land close to McDonalds.
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Old 7th Aug 2022, 9:53 pm   #9
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Default Re: PDP11/20 demo

PDP-10s were basically mainframes. DEC marketed them as DECSystem-10s. They were popular with universities and polytechnics, and were important in the early evolution of hacker and internet culture. DEC axed development to concentrate on VAX technology, something that caused a lot of resentment at the time. 36 bit word length I think, and 6.3 filenames crammed into 36 bits. Memory and disk space was expensive in those days.

The graphics for the movie Tron were done on a one-off prototype DEC-10 replacement.

https://en.wikipedia.org/wiki/Foonly
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Old 7th Aug 2022, 10:38 pm   #10
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Default Re: PDP11/20 demo

I was wondering if I remembered it wrong as a PDP10 but found this on wikipedia which matches what I remembered.

https://en.wikipedia.org/wiki/Lunar_...eo_game_genre)

I know it wasn’t connected to the PDP11 so it probably was the PDP10. I didn’t think it was big enough to be a mainframe.
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Old 8th Aug 2022, 3:10 am   #11
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Default Re: PDP11/20 demo

There certainly is a lunar lander game for the PDP11. In fact it will run on the GT40 graphics terminal which is a PDP11/05 + vector graphics display system in a special backplane -- it must be just about the only terminal that has a lights-and-switches frontpanel.

You play it with a lightpen, there are arrows to rotate left and right and a slidebar thing for thrust.
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Old 8th Aug 2022, 5:29 am   #12
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Default Re: PDP11/20 demo

Yes, but I know we were not playing it on the PDP11 so it was a PDP10 that we used to play it on. I was just not sure when Paul described the PDP10 as a mainframe, though its probably just a matter of scale and additional peripherals.
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Old 8th Aug 2022, 8:33 am   #13
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Default Re: PDP11/20 demo

Wiki article on the PDP-10, with pictures: https://en.wikipedia.org/wiki/PDP-10

They were still using one at South Bank Poly when I briefly worked there in the mid 80s.

I suspect you were playing Lunar Lander on a PDP-8. They were quite popular in college computer science departments in the 70s, and some soldiered on well into the 80s.

https://en.wikipedia.org/wiki/PDP-8
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Old 8th Aug 2022, 10:16 am   #14
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Default Re: PDP11/20 demo

Quote:
Originally Posted by Roland Huisman View Post
I still have to fix my 4KW core memory module, but at least it is complete.
Good luck with that! I saw the DEC service engineer repairing the core memory. Itís about 48 years ago, but as far as I remember it involved some very fine work on the wires running through the cores.
David
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Old 8th Aug 2022, 10:35 am   #15
Roland Huisman
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Default Re: PDP11/20 demo

Hi David,

Normally core is very trustworthy. Several others of my PDP8 and 11 machines run on core too... Once I have repaired the core module in my PDP8/L. That machine was in a very bad shape. (This machine was used for satellite navigation with the Transit satellite navigation system)

Many of the 512 diodes on the core stack were shorted. After replacing the shorted ones the machine worked for a little while and stopped again. (here you can see what happened) The memory contents became corrupt and the machine stopped working again. So I replaced all 512 diodes on the core stack and it still works fine. (The core stack was not the only problem, many other diodes and TTL chips were bad too... See restoration story on vcfed)

Now I have to fix one of my Teletypes and run Fortran on it. Where can I buy a box full off spare time?

Regards, Roland
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Old 8th Aug 2022, 2:12 pm   #16
Mark1960
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Default Re: PDP11/20 demo

Tried searching for equipment that they had at Durham and found this. So it looks like it was connected to a PDP11/10
http://etheses.dur.ac.uk/7635/1/7635_4700.PDF
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Old 8th Aug 2022, 2:42 pm   #17
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Default Re: PDP11/20 demo

That makes sense.
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Old 9th Aug 2022, 1:15 pm   #18
Roland Huisman
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Default Re: PDP11/20 demo

Nice!

I also have the PDP11/10 but it has an AR11 point/plot card. My system is a very small 11/10 the floppy drive is twice as big... Mattis Lind edited a version of SpaceWar to run on An AR11.

I've done more of less the same for the PDP8 spacewar which was made for an AX08, it now runs on the (also cloned) VC8E board set.

Regards, Roland
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