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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

electric_machinery@reddit

Very impressive!ย 
View on Reddit #77289740

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
View on Reddit #77022366

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!).
View on Reddit #77167383

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.
View on Reddit #77191355

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!
View on Reddit #77023100

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...
View on Reddit #77075396

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!
View on Reddit #77105826

Independent_Shoe3523@reddit

Not a true microcomputer, is that why it doesn't count as the first PC?
View on Reddit #76981425

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.
View on Reddit #76982241

Grumpflipot@reddit

16 Users? Wot?
View on Reddit #77019700

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!
View on Reddit #77020006

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.
View on Reddit #77024097

techman2692@reddit

In a really simplified term, it's basically the client/server setup we're more accustomed to in today's era.
View on Reddit #77131877

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.
View on Reddit #77028340

Independent_Shoe3523@reddit

So you don't need a monitor so much as a dumb terminal.
View on Reddit #76982321

samarijackfan@reddit

We had a teletype in high school. none of these fancy CRT monitors.
View on Reddit #76995967

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.
View on Reddit #76996371

oyvindhammer@reddit (OP)

That's right.
View on Reddit #76982530

Blah-Blah-Blah-2023@reddit

"Minicomputer" is the contemporary term.
View on Reddit #76983865

blakewantsa68@reddit

wow! I haven't seen one of those since about 1980!!
View on Reddit #77110371

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....
View on Reddit #77069026

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.
View on Reddit #77069538

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.
View on Reddit #77075265

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!
View on Reddit #77105402

mr_christer@reddit

Was this used with a typewriter terminal back in the day?
View on Reddit #77012388

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.
View on Reddit #77018107

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 )
View on Reddit #77075696

oyvindhammer@reddit (OP)

Haha lovely story, thanks!
View on Reddit #77102701

raytoei@reddit

The soul of a new machineโ€ฆ.
View on Reddit #77032906

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.
View on Reddit #77042056

HurryHurryHippos@reddit

R
View on Reddit #77033307

Laser_Krypton7000@reddit

๐Ÿ‘๐Ÿ‘๐Ÿ‘ Will you also compute some paleontology things with it ?๐Ÿ˜ Can you eventually post some pics of the inside pls ?
View on Reddit #76983409

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!
View on Reddit #77017516

zeissikon@reddit

What shell do you use ?
View on Reddit #77033027

jensgk@reddit

What is the association of this computer to paleontology?
View on Reddit #77022043

oyvindhammer@reddit (OP)

None whatsoever (only I'm a paleontology prof when not fixing minicomputers ๐Ÿ™‚)
View on Reddit #77022318

jensgk@reddit

Ahh. Great combination, both biological and electronic fossils :-)
View on Reddit #77026102

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?
View on Reddit #77015786

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.
View on Reddit #77018712

leRealKraut@reddit

Wow. Very nice.
View on Reddit #77023910

Grumpflipot@reddit

I played Hamurabi an a Commodore 3032 at school. This one looks way older.
View on Reddit #77018242

oyvindhammer@reddit (OP)

Aha, nice! It is an amazingly boring game, but perfect for showing the state of the art back then.
View on Reddit #77018925

LiqvidNyquist@reddit

Wow, that's impressive and really cool. And to find software that runs on it, even better!
View on Reddit #77003670

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.
View on Reddit #77017904

roz303@reddit

What a gorgeous machine! What's the fan noise like?
View on Reddit #77002710

oyvindhammer@reddit (OP)

It's ... quite bad, but that's part of the fun (my family is not so amused however).
View on Reddit #77017760

samarijackfan@reddit

No paper tape reader?
View on Reddit #76996004

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.
View on Reddit #77017699

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.
View on Reddit #77012759

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!
View on Reddit #77017313

jcmush@reddit

I saw the post and was going to recommend that. Itโ€™s a wonderful book. Congratulations on your project!
View on Reddit #77015956

BazuzuDear@reddit

Can you add some inside photos?
View on Reddit #76992520

oyvindhammer@reddit (OP)

Posted a photo in the geoup!
View on Reddit #77017099

Cwc2413@reddit

Very cool! I love these lesser known machines!
View on Reddit #77002073

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.
View on Reddit #76995814

healeyd@reddit

Awesome. Love the mid-century style on the panel. Like something out of 2001.
View on Reddit #76992433

hougaard@reddit

Good work!
View on Reddit #76991100

AllReflection@reddit

That is badass! ๐Ÿคฉ
View on Reddit #76990887

fuzzmonkey35@reddit

Dang
View on Reddit #76986257

GIVES_THANKS@reddit

Cool! Nice work!
View on Reddit #76984291

mrspelunx@reddit

Any extra hardware for the serial linkup?
View on Reddit #76980146

oyvindhammer@reddit (OP)

Just a cheap "FTDI chip" USB to RS-232 cable. The Nova has a standard RS-232 terminal port.
View on Reddit #76981193

kapitaali_com@reddit

whoa!
View on Reddit #76979716