From: (Device) Interfaces

This distinction is at the eletrical signalling level. However,
single-ended is limited to total bus lengths of 6.0 meters, while
differential can go up to 25 meters (SCSI-II). Differential is
generally more robust to noise and cross-talk, but the bus drivers are
more expensive. In theory no difference in transfer speed or
capabilities, but in practice the added noise margin could mean higher
_reliable_ transfer rates on your system, especially if your bus is
long.

Most disk drives and most low-end products are available only with a
single-ended interface. A few devices are available with either as a
purchase option, and a few are switchable by the user.

The cables and connectors are the same for both, though the pinouts
are (naturally) somewhat different.

Plugging a single-ended device into a running differential bus or
vice-versa may result in damage to one or more devices. Most newer
devices have fuses or protection circuits utilitizing the DIFFSENSE
signal to prevent device damage.

There are now recommended icons used to distinguish between the two:


single-ended                    differential
  /\                             //\
 /  \                           //  \
<   --                         <<   --
 \  /                           \\  /
  \/                             \\/

Converters do exist that will allow you to hook up single-ended
devices to a differential bus and vice-versa. People who have used
them say they work great, but in theory they shouldn't work :-).  As I
understand it, changing the signalling introduces delays in some of
the control signals that means that some devices could miss certain
signal transitions. The best advice is to borrow one and try it, and
see if it works in your system. One company's name is Paralan,
(619)560-7266.