> 
> With IDE drives you've at last one interrupt per xfer. With a decent
> SCSI adapter and driver you should be able to have serveral xfers per
> interrupt. Also with today's IDE controllers you still have to read/write
> registers on the PCI bus, before and after each xfer. This is slower than
> main RAM, of course. With good SCSI controllers read/write of registers

yes - but this additional load isn't big unless you have one slow CPU and
20 IDE drives.