Norsk Data got off to a good start, with their 16-bit 1967 NORD-1 mini - it had hardware floating point (48 bit) and virtual memory, and was the first to do so. Some 142 were made, and 10 survive. First one went into a ship for collision avoidance - real time control with high stakes. Lots of technical info here:
http://www.ndwiki.org/wiki/NORD-1
And even more in the manual (PDF) - it seems the page size was just 256 words and the virtual memory size 64k, compared to the physical core memory which could be as small as 4k. Paging was to disk or drum. There was also memory write-protection at a 1k granularity, or 1/16th of a larger core. It looks like the instruction set offered an 8 bit signed address field, for references relative to PC, to a base, to an index, or to sum of base and index.
Here’s one:
The company seemed to do very well all the way into the 32 bit era, but was initially anti-Unix and more hardware-centric than vertically-integrated, so the bubble burst and they went into decline. There’s a history article for the company on Wikipedia:
And then, in 1986 or so, they took their successful 32-bit ND-500 supermini from 1981 and knocked a few bits of address space off, to meet CoCom export controls. The machine allows a process to have up to 256Mbyte rather than 4Gbyte of space. Apparently this was a matter of snipping a wire - the ND-505 (PDF) is variously described as a 31-bit, 29-bit or 28-bit machine. Of course, the instruction set architecture is still 32 bit.
(This post prompted by @Tor’s introduction post.)
