> ...there is rumor that Bil Herd made a prototype that runs Z80 at full speed of 4MHz...
From the book, "On the Edge: the Spectacular Rise and Fall of Commodore," page 491:
"The [engineering] pair tried to evolve the C128 line, in case it enjoyed the same success as the C64. 'Frank [Palaia] and I each took half of the problem,' says [Dave] Haynie. 'He made a version of the C128 that ran a 4 MHz Z80. I made a version of the C128 with a slightly different MMU that gave 256K of built in memory.' Haynie called his proposed system the C256."
Ah, so it was Frank Palaia who made the 4MHz Z80 (and Dave Haynie who made the C256 MMU). I stand corrected.
I recall Bil Herd saying something like managers found about a secret ability (presumably in the original MMU) that would allow 256K and so made the team remove it... If Dave was responsible for the original, then it was probably real simple for him to put that feature back.