Quoting der Mouse <mouse@Rodents.Montreal.QC.CA>:

> How much do SCSI controllers typically know of SCSI (as opposed to the
> knowledge being in host software)?
>
> I suppose that depends on the hardware platform in question.  So here's
> why I ask....
>
> I was thinking about connecting two SCSI buses with the data wires
> switched around, so that one bus's D7 (and therefore ID 7) isn't the
> same as the other's.  This would allow me to take two machines with
> internal disks and plug them together through their external SCSI
> connectors.  (For the moment, I am prepared to depend on the human
> layer to avoid problems from both hosts trying to access a drive at the
> same time.)

It would be easier to just reprogram the SCSI controller to use a 
different ID. Most of them support it.

More importantly, the arbitration isn't going to work right if both systems
think they're at ID 7 and the other is at ID 6.  They will both try to use the
bus at the same time.