> Then, as a young engineer, I worked in a large mainframe computer system based on Z80.

This sentence threw me a little bit. Which mainframes were based on the Z80? I'd love to know more about that.

If it wasnt some mostly custom system it was probably an HP 64000 Logic Development System. Which used Z80s to run user facing software and control the actual mainframe. I doubt it was a pure Z80 "mainframe". Loved to be proved wrong though!