hckrnws

The grid is 0.1" holes because that's the spacing of most components; it's a bit like perfboard. If you're asking why they used a grid instead of a normal-style PCB, I'm not sure. It probably makes manufacturing the boards much easier since you can drill the holes with an assembly line rather than one at a time. The traces go between the holes; the traces are very narrow, so two traces can fit between a pair of holes. That's probably the tradeoff, that your traces need to be very precise and you probably need more layers because of all the holes in the way. The layout was probably done with CAD; PCBs with CAD go way back. IBM was doing circuit boards with CAD back in the early 1960s, using a flying spot of light to draw out the PCBs on photoresist.

> The PCB construction is curious (which you say is multi-layer) - why use a grid of 0.1" holes?

The claim is multi-layer, but I seriously doubt that. I suspect that these are two-layer boards.

And if that's the case, the pattern is most likely because the holes precede the etch. And possibly precede the copper deposition so that the copper deposition can coat the insides of the holes.

And the holes are in a regular pattern because CNC simply wasn't a thing yet. You probably had some fixed array of drill bits that were used to make the holes in a very strict fixed automation fashion.

Do we know anything about the software that ran on it? What language it was developed on, what host platform was used for development, etc? Does any of the code survive?

When you say that the 125 added memory management, what does that mean a little more specifically? My guess is either PDP-11/z280 style paging without page tables (the 16 bit address space makes just having enough IO registers to cover the address space tractable) or some simple segmentation hardware, but it'd be neat if there was another hardware object capability system I didn't know about.

What frequency did it it cycle at? Any idea how many instructions per second it could process?