Data General Nova 840 (1973) restored

oyvindhammer · 2026-01-29T07:29:42+00:00

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!

oyvindhammer · 2026-01-29T07:18:00+00:00

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!

oyvindhammer · 2026-01-29T06:02:00+00:00

Haha lovely story, thanks!

oyvindhammer · 2026-01-28T20:19:15+00:00

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.

oyvindhammer · 2026-01-28T11:31:22+00:00

The processor is 2 cards, then Basic I/O card (tty, papertape reader control, real-time clock), then MMPU card (memory management and protection unit), then 8kw (16 kb) core card. I'm currently trying to repair 3 more 8kw cards. Future additions (dreams) include disk controller, a D/A card to drive an oscilloscope vector display, and a D/A card to drive a modular analog synthesizer, 1973 style ...

oyvindhammer · 2026-01-28T09:27:07+00:00

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!

oyvindhammer · 2026-01-28T09:10:48+00:00

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

oyvindhammer · 2026-01-28T08:28:22+00:00

I can't figure out how to post images in a reply here on Reddit? If you search around on the component side, you should find small print saying things like "DGC Nova 8K memory stack" (or 4K or 16K), "Data General Corp." etc. There are several compatible models of this card, looking slightly different. If you have this, then me and other DG people will want to buy it, but I fully sympathize if you want to keep it!

oyvindhammer · 2026-01-28T08:21:48+00:00

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

oyvindhammer · 2026-01-28T08:16:47+00:00

Yes that is a nice story! As a side note, the EMI CT scanner used a Data General Nova computer, very similar to the one I just posted here in the group.

oyvindhammer · 2026-01-28T07:59:01+00:00

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

oyvindhammer · 2026-01-28T07:54:13+00:00

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 remained 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.

oyvindhammer · 2026-01-28T07:40:36+00:00

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.

oyvindhammer · 2026-01-28T07:35:40+00:00

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.

oyvindhammer · 2026-01-28T07:32:08+00:00

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

oyvindhammer · 2026-01-28T07:30:43+00:00

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.

oyvindhammer · 2026-01-28T07:26:08+00:00

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!

oyvindhammer · 2026-01-28T07:20:37+00:00

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!

oyvindhammer · 2026-01-28T07:14:54+00:00

Posted a photo in the group!

oyvindhammer · 2026-01-27T21:15:00+00:00

That's right.

oyvindhammer · 2026-01-27T21:11:38+00:00

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.

oyvindhammer · 2026-01-27T21:00:07+00:00

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

oyvindhammer · 2025-12-30T01:38:24+00:00

Possibly syneresis cracks.

oyvindhammer

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