
By initiating a DMA xfer.  :)

Seriously, busmastering adapter have their own DMA ability, they don't use
the motherboards on-board DMA(which is *MUCH* slower).

ISA has no bus arbitration, so if two busmastering cards in 1 ISA system
try to do DMA xfers on the same DMA channel the system will lock or 
crash.(I forget)

Their are 8 DMA channels in an ISA system. 0-7. 0-3 are 8-bit & 4-7 are
16-bit.

The system uses DMA 0, a SoundBlaster uses DMA 1.

I could buy a busmastering XGA-2 video card & a busmastering SCSI HA.

In order for them to work properly, I would have to find out what DMA
channel the XGA-2 card uses and then simply configure the SCSI HA to
use a different DMA channel for its DMA xfers.

I don't know if multiple DMA xfers can go on at the same time on ISA.
I'm not sure if they can on EISA systems either.

I do know that on EISA/MCA systems, you can allow BM cards to use the
same DMA channel.