The Blue Lightning CPU is an interesting beast. There is not a whole lot of information about what the processor really is, but it can be pieced together from various scraps of information. Around 1990, IBM needed low-power 32-bit processors with good performance for its portable systems, but no one offered such CPUs yet. IBM licensed the 386SX core from Intel and turned it into the IBM 386SLC processor (SLC reportedly stood for “Super Little Chip”).
Later on, IBM updated the processor to support 486 instructions. It is worth noting that there were still the SLC variants available—nominally a 486, but with a 16-bit bus.
The licensing conditions reportedly prevented IBM from selling the SLC processors on the free market. They were only available in IBM-built systems and always(?) as QFP soldered on a board.
A very unique processor from the days Intel licensed others to make x86 chips, even allowing them to improve upon them. Those days are long gone, with only AMD and VIA remaining as companies with an x86 license.