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Rationale
Sooooo, why would a  |D|I|G|I|T|A|L|  PDP-11 / VAX computer systems collector want to keep a Data General machine? As you can read on the Wikipedia page, the company Data General was founded by 4 men, 3 of them came from DIGITAL. They did not agree how DIGITAL set out to develop the PDP-11 as follow-up of the successful PDP8. Ken Olsen, one of the founders of Digital Equipment Corporation, speaks of this time as a "black page" in the history of DIGITAL. That is the link between DEC and DG and my rationale to keep the NOVA 3 in my collection. Besides, the NOVA 3 has a nice "blinkenlight" console, always an eye-catcher when the machine is running

I got the following information from Peter Simpson. Peter used to work at Data General.
The Data General architecture, NOVA especially, shows its PDP-8 heritage rather clearly. The story is that DEC had two parallel teams working on the successor to the PDP-8, one team working on what became the PDP-11 and the other team, lead by de Castro, working on something that was more PDP-8-like ... which became (with not too many changes, the story goes) the NOVA.
de Castro was _persona non grata_ at DEC. Apparently, when he left, he burned ALL the bridges.

If you pull a random board, you will find a 4-digit model number and a brief name near the handle. The labels on the board handles tell you the serial number and the revision level.
The serial number is a "005-" number. This is the tested assembly number and represents the board, as it is configured and tested. The revision level are any ECOs (Engineering Change Order) numbers added above the rev number, letter and 3 digits(?).
001- number  ::  schematic part number (good luck getting this!)
003- number  ::  BOM number?   PC artwork number?   (memory is vague, it's been 30 years!)
107- number  ::  the artwork number

Everything that DG built from raw parts had a 005- number. Cables, boards, mechanical assemblies and complete, shippable products. Boards that have TWO 005- numbers have the numbers for tested and untested assemblies. Testing might include adding firmware or options (Floating Point or extended addressing). At least, I think that's the way it worked. One number for the base board, one for the configured assembly. A bold T followed by a 005- number (T 005-) is the tested assembly number.

Data General was famously paranoid. Many of the ICs (all on the older PCBs) will not have manufacturer part numbers, but DG part numbers - the ICs were 100- numbers of which 100-799 was a 7400 gate (IIRC). It's probably marked "799". 100-1253 was a 74LS244 (again IIRC)...   This was so third parties could not copy the boards and sell them or service them cheaper than DG could.  Remember that Data General made way more money servicing their equipment, than they did by selling it. This was before the age of generic hardware, and keeping things secret meant the customer was locked in.

Links to other sites 
I found some dead links and some useful links to sites with information about Data General and their systems.

• Bruce Ray's Simulogics site dedicated to preservation of DG hardware, software and documentation
• Carl Friend's Minicomputer "Museum" with lots of DG systems information
• Data General NOVA 3 Computer system with some peripherals
• Data General NOVA 4, but a lot of useful information and links
• The tale of bringing a NOVA 3 to a new home in "down under"
• The Wikipedia page about Data General (must read! great introduction to DG and lots of info)

Some general information
As not much is available on-line, here is some general information on the Data General systems. Most of the information comes from Bruce. If you have questions about your DG machine, send him an email. Bruce is a really great guy and very helpful.

The boards inside the system chassis are installed horizontally. You already know that these boards are quite large, their dimensions are 15" x 15". To prevent bending, all boards have a horizontal card board stiffener along the front side of the board. Further, as these boards are mounted quite close to each other, every board has a thin sheet of insulating fibre material which is attached to the board with one screw secured in the horizontal stiffener.
On the horizontal stiffener are several labels glued. Make notes of these, they are important! To identify a board, the numbers etched in the copper are useless, because Data General did not have an official cross-reference for board artwork number to product or assembly numbers. So, forget the "107-xxxxxx-yy" number in the copper etch on the board. The real key is the "T 005-xxxxxx-yy" number - the "Product Number". For example, the tape drive controller card that Geert pulled from the Eclipse has the following labelling on the stiffener.

This tells that this board is a product 005-015289, revision 03, which is a "Nova/Eclipse Streamer Tape Drive 6125 Controller". Bruce says "Yes, it - like most controllers - can be used by both Nova and Eclipse computers."   That is good news, because that means that this tape controller board pulled from the Eclipse can be installed in my NOVA 3 to hook up the Model 6125 tape streamer, in the future!