Apple is abandoning SCSI for
FireWire on the high end
and
USB on the low end, and many of their machines have
IDE for internal drives. All of these technologies are smaller and cheaper
than on board
SCSI.
Sun is still
using
Ultra Wide SCSI in some of its servers, but is
using
IDE in its low end workstations, and
Fibre channel
on its very high end systems.
Apple does support scsi still, but in the form
of a firewire to scsi adapter (very expensive, oops), or a PCI SCSI add on card. This is (obviously) only available in the tower systems with
PCI slots.
The biggest problem with SCSI is that it requires proper termination,
and even some hardware vendors can't get this right. IDE doesn't need
termination (as much), because the bus length is shorter and there are fewer drives
on the bus. USB and Firewire are prefered over scsi probably due to simpler
bus connection, smaller cables, and hot plug capability, which is more
appropriate for portable zip drives, scanners, cameras, etc.
Meanwhile, much of the functionality of scsi has been subsumed into IDE.
SCSI has a much higher per-command overhead, which is balanced out with its
superior ability to issue multiple simultaneous commands, which
explains one of the reasons why scsi usually outperforms IDE in multiuser
conditions, even when their bandwidths are similar. Firewire is fast, and beats
older scsi, but newer scsi still is faster with its multiwire parallel bus.
SCSI is a good alternative when you need more than IDE or firewire can give, but still can't afford fibre channel.