#z80 #retrocomputing aficionados: what was the 'best' Z80 machine of the #eightbit era? I mean the most sophisticated and capable machine, in terms of offloading video, sound and anything else to custom chips. An #MSX second or 2+ generation, perhaps?
@fluidlogic Best was the Commodore 128. Not only did it offload video, sound, and I/O to custom chips, it also offloaded CPU tasks to a custom chip. Typically, the Z80 only needed to work for a few cycles per power up.
@isaackuo that's really fascinating. I had no idea the #Commodore128 had a #Z80 CPU in it.
As you say, the machine started from the Z80:
When the C128 is powered on, the Z80 is active first and executes a small boot loader ROM at $0-$FFF to check for the presence of a CP/M disk. If one is not detected, control is passed to the 8502 and C128 native mode is started.
...but the Z80 is also described as 'the second CPU':
The primary CPU, the 8502, is a slightly improved version of the 6510, capable of being clocked at 2 MHz. The second CPU is a Zilog Z80 which is used to run CP/M software, as well as to initiate operating-mode selection at boot time.
The machine was primarily designed around the 8502:
the Z80 processor runs at an effective speed of only 2 MHz. [...] the C128's system bus was designed around the 65xx CPUs. These CPUs handle data and memory addressing very differently from the Z80. CP/M [passed] control to the 8502 for any I/O or interrupt processing.
@fluidlogic To clarify, my answer was tongue-in-cheek -- something that would only be obvious to someone already familiar with the C128.
To call the C128 a "Z80" computer is silly, but I couldn't resist making the joke when you defined your criteria as offloading graphics, sound and _other stuff_ to custom chips.
In terms of how much work the computer does per Z80 cycle, the C128 does indeed win. But at what cost?
@isaackuo yeah, I was deliberately being vague, mentioning "other stuff"! I had I/O in mind, so it's really interesting that that's exactly what the 128 relied on the 8502 for, while in CP/M mode! I had no idea!
All this is to say that the 1980s Cambrian explosion of microcomputers, made possible by the sheer inventiveness of their designers working within cost and capability constraints, was a truly unique time.