alt Hacker News"Simple" is really not a word I would associate with the Z80 ;)
The ISA is quite messy because of the backward compatibility requirement with the Intel 8080 (e.g. the Z80 had to fill undocumented gaps in the 8080 opcode encoding map with new instructions, four of which were prefix instructions to unlock additional instruction 'subsets' (DD/FD for replacing instructions involving the HL register pair with indexed addressing modes via the IX/IY registers, and ED/CB prefixes for adding two entirely new opcode blocks).
If the Zilog engineers would have been free to design their own ISA I'm sure they would have been able to come up with a much more elegant design.
Also the Z80 had more than twice as many transistors as the 6502 (8500 for the Z80 vs 3500 for 6502).
I still prefer programming the Z80 over the 6502 though :)
Replies
> If the Zilog engineers would have been free to design their own ISA I'm sure they would have been able to come up with a much more elegant design.
That's an interesting idea. They were previously part of the team that designed the 8080 so they must have been very familiar with the ISA and the design philosophy.
I'm sure they'd be able to come up with improvements but how much more elegant it would have been is hard to say.
> If the Zilog engineers would have been free to design their own ISA I'm sure they would have been able to come up with a much more elegant design.
Since Zilog was founded by former Intel engineers, they were probably the ones who helped design the 8080 in the first place?
I am simplifying a lot since there were much more chips involved... but 3500 transistors to have countless hours of fun to play NES games really puts things into perspective
My 5090 has 92 billion transistors (I dont say they dont bring fun)