There are several completely different kinds of DMA:
- chipset bus DMA - arbitrated by Agnus
- CPU bus DMA by Zorro II/III cards - arbitrated by (Super) Buster - since the CPU can access the chip bus this also includes chipset bus DMA
- CPU card DMA by onboard devices (=SCSI HBAs) - arbitrated by some onboard facility
- PCI busboard DMA is somewhat similar to the CPU card variant, but it seems to be very hard (impossible?) to DMA from PCI to Zorro, so it's from PCI to PCI only
A Z3 card is able to DMA to chipmem, but would be rather slow (you'd have to sync down to the chip bus plus wait for a chip DMA slot to come up). AFAIK there are no Zorro NICs that DMA.
