Zorro3 is older than PCI. Dave Haynie, system architect at Commodore was planning to use PCI in the next Amiga chipset instead of Zorro3/4. PCI wasbuilt from the start as a faster thing, Zorro3 was a jump from 16bit (as in Zorro2) to 32bit access. PCI was defined with a 33MHz bus clock, Zorro3 is asynchronous meaning it has no bus clock. In theory this could allow better improvements, as asynchronous things can talk to each other as fast as the slower of the two devices can possibly go, so you aren't necessarily limited by a predefined clock speed. The problem is that Buster was never updated to go faster than the rev 11 does, so no Zorro3 expansion card can be used faster than Buster can go, as Buster sits between the card and the rest of the system. At the same time, I don't believe any existing Zorro3 cards are capable of going faster than Buster anyway, so there's almost no point in speeding up Buster anymore. The only real benefit we'd see at this point is possibly the PCI bus adaptors could be updated to allow faster PCI bus access from the Amiga system. That'd be cool, but probably not cost effective, and the existing Mediators/Prometheuses may not be able to be updated to significant faster Buster use anyway. I'd thought of tinkering around and making a replacement for Buster in an FPGA chip, but couldn't find a suitable verilog simulator that I could afford for debugging the logic design of what I would have done, and it went nowhere. I'd still buy such a thing if someone made one, but my interests have moved on to other things, plus I've ordered an AmigaOne, so I wont' need to spend the time to build it myself anymore.
The PCI equivalent of "Buster" was generally the "north bridge", but mroe recent things have the north bridge outputting a hypertransport bus that conencts to the "south bridge", and PCI then comes out of the south chip. Older south bridge chips talked across a PCI bus to the north bridge, and south had an ISA bus, and usually IDE, ethernet , serial/parallel, etc. things came from the south bridge. As time moves on, more and more of that stuff is being combined in withthe north bridge stuff to reduce number of chips, and thus make it cheaper to manufacture the motherboard.
