The 8-bit Z80 is dead. Long live the 16-bit Z80

The eZ80 is a 24-bit Z80! I have one of those AgonLight 2 boards coming in the mail. Of all the machines that revisit the 8-bit age I think this is really the best because it has one foot in the BBC Micro world of a color graphic Z80 machine and another the the CP/M world where a lot of serious software is available.

Not only is it two orders of magnitude faster than any CP/M machine back in the day but it has a memory model good enough that it should be possible to build an OS that can run multiple CP/M applications at the same time.

Not sure I understand the point of a 24-bit cpu. If 16b-wide registers don't cut it, the difference between 24 or 32 bit wide registers can't be that much in terms of transistors or cost, right?

You can have address lines for say, 20..24 bit wide memory (1MB & up), but still have a full 32 bit architecture internally.

Or (if lowest cost/power is desired) the other way around: a 16-bit cpu with >16 external address lines, handled by built in MMU.

On the R800: this is indeed a nice chip. ASCII developed it for the MSX Turbo-R, but (afaik) never bothered to put it on the market for use elsewhere. Don't think I've ever seen a datasheet of it, either.

Juno probe used Z80 architecture for part of it.