The B8500 line derives from the D825, a military computer that was inspired by the B5000.
The B8500, designed in the 1960s, was an attempt to merge the B5500 and the D825 designs. The system used monolithic integrated circuits with magnetic thin-film memory. The architecture employed a 48-bit word, stack, and descriptors like the B5500, but was not advertised as being upward-compatible. The B8500 could never be gotten to work reliably, and the project was canceled after 1970, never having delivered a completed system.
Read more about this topic: Burroughs Large Systems