The original Kaypro-II from 1982..
It is STILL is awesome design.
With one interesting flaw:
Andy Kay wanted to rush this model to the market, and the developpers couldn't find a proper VDU controller chip in time. Well, said the hardware design-team: let's make the VDU controller using discrete hardware (bunch of standard TTL IC's), and write the screencontrol code in the FIRMWARE!! And so they did!!
Using a Z80 mnemonic debugger on the code in the 4k EPROM, you can clearly see how a character is printed on the screen, and it is sloooowwww!!!!
For instance CLS (Clear Screen) is performed in a quite rudimentary way:
by filling the screenmemory with $20 (space) characters!!
VERY fast terminal programs were simply TOO fast for this hardware/firmware solution.