A brief diversion: the NRI-832

Still waiting for parts for debugging and repairing the Imlac to arrive.  (The protoboards for the extender cards arrived today, but I'm still waiting on the edge connectors...)  Got an IC tester (a Sunshine IC-301) for cost of shipping that I've used to great effect in weeding out the easily-detected dead ICs from the core memory control boards, but that's about all I've accomplished in the last couple of weeks.

My NRI-832

So instead, today I'll talk about my latest acquisition, an NRI-832 computer.  This computer was offered as a kit as part of a correspondence course from the National Radio Institute in 1971-1972, making it one of the earliest (if not the earliest) commercially available computer kits.  (It was a contemporary to the Kenbak-1, for example.)  The NRI-832 used approximately 75 integrated circuits to build an 8-bit processor (with a 5-bit address space) featuring a simple but adequate instruction set.  16 sets of 8 toggle switches on the front panel provided read-only storage for 16 instructions, and an additional 16 bytes of actual RAM could be added to the system (without this expansion, the system had only 1 byte of read/write storage).  The intent of the kit was to teach the basics of computer design and programming and while it was a very limited system it was still a computer one could have at home, and in 1971 that was nothing to sneeze at.  The kit retailed for $503.

The guts -- 70 ICs or so that implement a very simple CPU

I snagged this off of eBay for what I consider an amazing price given the computer's historical significance and rarity; every now and then you just get lucky.  This particular specimen is going to need a bit of work as it appears that assembly was never completed by its original owner.  Most notably missing is the PCB that holds the 128 toggle switches for program entry, but it's also pretty clear that a lot of the wiring was never completed.  But on the plus side, all of the logic is present and schematics and manuals are available so it's not an impossible task.  Building the toggle switch panel is going to be time consuming, involving a lot of soldering, but it's not difficult.

The front panel, outlining the instruction set

It looks like it should be fun to play with once it's up and running again; it'll be a nice exercise in minimalism to see what can be done with just 16 bytes of ROM and 16 bytes of RAM.

There's not a ton of NRI-832 related resources out there on the 'net, but the NRI-832 technical reference (and a javascript emulator!) is available on this blog if you want to know all the nitty-gritty.

Next time I hope to have made some small progress with the Imlac... time will tell.  In the meantime, keep on chooglin'.

Individual light bulbs for each bit in the IR/PC registers

The "ROM," originally consisting of 16 sets of 8 switches; currently missing.