Some (possibly) interesting comments:
- "later I think TI made (or tried to make) a plug-in card version of the TI Explorer for Macs" - this was the MicroExplorer NuBus card for Mac II-series machines, which was somewhat popular. Symbolics also built a NuBus Lisp machine board for Macs.
- "This machine had one of the largest CPUs ever made until that time, something like half a million transistors." The original version of the Explorer (Explorer I) implemented the CPU in TTL logic (plus microcode ROMs and PROMs to implement some logic functions) on two large NuBus boards, the integrated version was later used in the Explorer II and MicroExplorer.
- "the entire computer division was sold off to HP soon after I left" - one of the sad stories, HP destroyed a number of companies after they took over. In addition to TI's computer department (the TI990 16 bit machines were sold to some other company), Apollo, Tandem and DEC (via Compaq) suffered a similar fate.
- "Pretty sure the sale included a sweet little Unix box". This was the TI1500, a 680x0-based asymmetric multiprocessor machine running TI System V (SVR3) with some pretty advanced concepts for its time (such as software RAID/striping), which was also based on NuBus. You could add a TI 68020 CPU board to an Explorer and run Unix on the side. I used to service and admin TI1500 machines as a student and am possibly the last person on Earth with the source code for TI's version of gcc (a horribly hacked version of gcc-1.37 in which the TI-specific code was #ifdef'd into the hp300 backend...). Back in the 90s, I had to request the code from TI in the US (after the division was sold to HP) and received a QIC tape with the gcc/binutils code some weeks later.
The whole NuBus system was based on the NuMachine concept developed at MIT and later Western Digital (https://en.wikipedia.org/wiki/NuMachine). TI bought the rights to NuBus in 1983, Apple and NeXT later adopted the system for their 68k machines. It would be interesting to know why they didn't go with Motorola's own VME bus.
Fun trivia: Swissair used to run their whole booking system on TI Explorers and for some years in the 90s tried to buy every used Explorer system that was available to keep their systems running after the hardware was discontinued (http://lemonodor.com/archives/2002/10/ti_explorer_fam.html).