In a message to Anthony May about amazing facts!, Rod Speed said:

RS> The general idea is that the OS just needs to ensure that the HA
RS> never needs to DMA into anywhere outside the 16MB block. Just
RS> how effective it is in practice depends on other considerations
RS> like virtual DMA services too, the question of the
RS> correspondence between physical memory addresses and virtual
RS> ones.

Yeah, I'd pretty much figured that.  Its totally up to the driver to
make sure things stay below 16mb.

I was chatting to Brenton last night, specifically about the adaptec
ISA cards.  Aparently they are much like video cards I take it, and
do all dma xfers in an 8k window in UBM area.  In which case, if you
use an adaptec ctrlr and driver, there'd never be a problem with
>16mb ram

'tnt, Anthony.