Data General Nova 840 (1973) restored

Posted by oyvindhammer@reddit | vintagecomputing | View on Reddit | 63 comments

Data General Nova 840 (1973) restored

Eight months of massive repairs, more than 20 vintage chips replaced, in addition to broken caps, lamps, switches, transistors, but now my Nova 840 from 1973 is as good as new! Here running BASIC and the classical game Hamurabi, also from 1973. Using a Windows laptop as terminal, not nice I know, repairing a 1977 CRT terminal now!

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63 Comments

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electric_machinery@reddit

Very impressive!

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jensgk@reddit

Impressive. And so nice looking! How much RAM does it have? What is the speed of this? Have you run any benchmarks? Eg. https://en.wikipedia.org/wiki/Rugg/Feldman_benchmarks

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oyvindhammer@reddit (OP)

I tried those benchmarks! The Nova is not bad - it runs benchmark 4 at 3.8 seconds (with floating point), while Commodore 64 clocks in at 19.5 s. And the Nova is 9 years older (of course also a bit more expensive!).

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jensgk@reddit

That is really amazingly fast, I would never have thought that. It must be a combination of a really fast BASIC, and also a very good CPU.

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oyvindhammer@reddit (OP)

Thanks! At the moment only 8 kwords (16 kbytes), but I'm repairing more cards and hope to get up to 32 kwords. In olden days it had 64 kwords but then only through an MMPU (still working). It's a true 16-bits machine. Instructions are either 800 ns or 1600 ns (those that read or write core). Hardware multiply/divide. I will try to do some benchmarking, thanks for the link!

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zondance@reddit

Man learning how the MMPU worked was also WILD. Coming from my C=64 and early PC's I was so mind blown about mapping this memory around...

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oyvindhammer@reddit (OP)

Exactly. The MMPU is rather difficult. So far I'm only using it in "transparent" mode, just passing addresses through, but even that was broken so I had to replace a couple of chips in the MMPU also. You and I are the only people I know so far who have serviced an 840 MMPU!

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Independent_Shoe3523@reddit

Not a true microcomputer, is that why it doesn't count as the first PC?

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oyvindhammer@reddit (OP)

Exactly, this is not a microcomputer. It does not have a microprocessor but hundreds of little chips, each with a few logic gates. And magnetic core memory. It is a thing of great beauty, power and complexity. And this machine served 16 simultaneous users in its youth, so it is not a personal computer either.

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Grumpflipot@reddit

16 Users? Wot?

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oyvindhammer@reddit (OP)

Yes, 16 serial ports connected to 16 terminals, teaching programming to college classes. They would not get much memory or CPU cycles each!

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leRealKraut@reddit

This concept was also very strange for me. I grew up with a Pentium II. The concept of scheduled CPU time was never properly explained to me. As with terminals, tty and a lot of other stuff.

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techman2692@reddit

In a really simplified term, it's basically the client/server setup we're more accustomed to in today's era.

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Independent_Shoe3523@reddit

They send their programs to the computer and when the computer has time, it runs the program and sends the results back to the dumb terminal.

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Independent_Shoe3523@reddit

So you don't need a monitor so much as a dumb terminal.

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samarijackfan@reddit

We had a teletype in high school. none of these fancy CRT monitors.

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Independent_Shoe3523@reddit

I used those once or twice in a computer class when I was a freshman in college. There were never enough CRT terminals to go around.

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oyvindhammer@reddit (OP)

That's right.

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Blah-Blah-Blah-2023@reddit

"Minicomputer" is the contemporary term.

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blakewantsa68@reddit

wow! I haven't seen one of those since about 1980!!

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zondance@reddit

The Nova 840 & 1200 were the computers I was trained in 93 to maintain in the Air Force. These were our comm multiplexers at Cheyenne MT aka NORAD. Very cool to learn for the AF to teach me how a processor worked at the logic gate level clock cycle at a time on learning Octal....

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oyvindhammer@reddit (OP)

Fantastic - great to hear from a real Nova user, thanks! Astonishing that the Air Force was still using Novas in 1993, but yes they were known for being rugged and dependable, ar least compared with many other brands at the time.

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zondance@reddit

So the AF was working on transitioning off of them while I was there but they project was over budget and the new system that was software biased vs hw was underpowered I was told. (who knows). But you might like to know... Us techs took our first part of Electronics school at the standard AF electronics school at Keesler Air Force Base in Biloxi,MS. Then any of us that were 327R (327 computer maint, R is your going to Cheyenne MT). Were then sent along to a Colorado Springs (AF) extension school. This is where we learned to diagnose the Nova 800/1200 systems down to the chip/logic gate level. After graduating that. We were then once again split up and sent to the Mt to our duty stations. Board level repair shop - they cold diagnose/repair 80-90% of issues with boards and send them back out to be to be use.... (sometimes you would get a bad board and keep getting bad boards lol) Comm Mux - This is where I was stationed, we took all the data in from the radar sites, did some processing and sent it along to the next system. lol I dont really know what it did, I was just a bottom end Airman. This was mostly Nova 840s. Console Repair - These were the people that went into the actual command center and anywhere else that had consoles our user other devices. This job took a higher clearance and they mostly repaired Nova 1200 systems. Amazing systems to be able to learn all this tech on.

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oyvindhammer@reddit (OP)

This is fascinating. And so nice to hear from another person who has been through all the gates of the Nova840. I feel it was a gift that so much was broken in my machine, so I had to follow almost every signal line in there with my scope for months and learn all the details of such an amazing design. I'm almost hoping that something more will break so I can dive in there again!

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mr_christer@reddit

Was this used with a typewriter terminal back in the day?

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oyvindhammer@reddit (OP)

Yes, typically ASR 33 teletypes. They are slow, noisy, and now very rare. But after ca. 1975, CRT terminals were gradually taking over. I'm working on a Datamedia CRT terminal from 1977, that was actually used on this machine towards the end of its active lifetime.

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zondance@reddit

Also we used to have a drum printer in the AF that we would print memory dumps to. We had contractors that would READ THE OCTAL and then tell use oh ha you have a bad chip that needs to be fixed.... I remember them printing a dump and telling me I needed to go stand somewhere else as I was not cleared to be around the OCTAL code :D (like I am going to be able to read what is coming off the printer :D )

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oyvindhammer@reddit (OP)

Haha lovely story, thanks!

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raytoei@reddit

The soul of a new machine….

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cosmo7@reddit

I think this was a few generations before the Fountainhead in *Soul of a New Machine*, but awesome reference to drop. Anyone who likes this sub would really enjoy the book.

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HurryHurryHippos@reddit

R

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Laser_Krypton7000@reddit

👍👍👍 Will you also compute some paleontology things with it ?😁 Can you eventually post some pics of the inside pls ?

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oyvindhammer@reddit (OP)

Thanks, have posted an image in the group. Haha yes actually I might try to reproduce some classical computational paleontology work from the 1960s, especially Raup's beautiful CGI of seashells. Just need to make a vector display with an oscilloscope, should be relatively straightforward!

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zeissikon@reddit

What shell do you use ?

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jensgk@reddit

What is the association of this computer to paleontology?

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oyvindhammer@reddit (OP)

None whatsoever (only I'm a paleontology prof when not fixing minicomputers 🙂)

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jensgk@reddit

Ahh. Great combination, both biological and electronic fossils :-)

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leRealKraut@reddit

It is wild to me, that a 1973 Computer still used Manual switches and lamps as a Maschine Terminal. Did you enter a bootloader manually?

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oyvindhammer@reddit (OP)

Yes this is one of the last computers with glowing lamps (half of them burned out so I had to get new ones, from Chechnya of all places!). But similar consoles with LEDs were common on mini- and microcomputers throughout the 1970s. The console is a gift from the gods when debugging the hardware! The Nova has a tiny bootstrap loader in ROM, which loads a slightly larger binary loader from the serial port (in my case), which then loads e.g. stand-alone BASIC.

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leRealKraut@reddit

Wow. Very nice.

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Grumpflipot@reddit

I played Hamurabi an a Commodore 3032 at school. This one looks way older.

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oyvindhammer@reddit (OP)

Aha, nice! It is an amazingly boring game, but perfect for showing the state of the art back then.

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LiqvidNyquist@reddit

Wow, that's impressive and really cool. And to find software that runs on it, even better!

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oyvindhammer@reddit (OP)

Oh there is a fantastic web site called novasareforever.org with a ton of software and documentation. And there is a very helpful, small community of Data General enthusiasts.

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roz303@reddit

What a gorgeous machine! What's the fan noise like?

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oyvindhammer@reddit (OP)

It's ... quite bad, but that's part of the fun (my family is not so amused however).

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samarijackfan@reddit

No paper tape reader?

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oyvindhammer@reddit (OP)

Ah you hit a sore thumb there. No. I'm looking for one, and there are some OK ones on eBay etc. Problem is that I would need some tapes to read, and then I would need a paper tape punch, and they are much rarer and very expensive.

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WingedGundark@reddit

Whoa, that is something you don't see everyday! What is your mass storage solution here or how do you exactly load software in this thing? If you haven't already, I highly recommend reading The Soul of A New Machine. It is about the development of Eclipse mini computer in Data General. It is more about people than technology, but still a well written and a fascinating glimpse to computer engineering in mid to late 70s.

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oyvindhammer@reddit (OP)

Yes it's on my to-do list to read that book! No mass storage yet - just uploading to core memory through the serial port. In the old days this would be using the paper tape reader on the Teletype. Data General had good solutions for such simple "stand-alone" operation without disk. And it helps that core memory is not deleted on power-down!

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jcmush@reddit

I saw the post and was going to recommend that. It’s a wonderful book. Congratulations on your project!

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BazuzuDear@reddit

Can you add some inside photos?

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oyvindhammer@reddit (OP)

Posted a photo in the geoup!

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Cwc2413@reddit

Very cool! I love these lesser known machines!

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samarijackfan@reddit

Thanks for the picture. I programed one of these in my high school computer class. I could not remember what system it was. Wow, a blast from the past.

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healeyd@reddit

Awesome. Love the mid-century style on the panel. Like something out of 2001.

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hougaard@reddit

Good work!

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AllReflection@reddit

That is badass! 🤩

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fuzzmonkey35@reddit

Dang

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GIVES_THANKS@reddit

Cool! Nice work!

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mrspelunx@reddit

Any extra hardware for the serial linkup?

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oyvindhammer@reddit (OP)

Just a cheap "FTDI chip" USB to RS-232 cable. The Nova has a standard RS-232 terminal port.

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kapitaali_com@reddit

whoa!

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