[rescue] SCSI Cables/Term: LVD -vs- HVD -vs- FW/SE

[rescue at sunhelp.org]

Over the last several years, I'm discovering that I've accumulated
a few more odd cables and terminators than I thought.  I've
been troubleshooting some SCSI problems on two systems,
though, and I want to make sure I understand the differences
and effects of cables that are labeled in different ways.

Here's what I *think* the answers are (based on some testing
and some memory):
 - If I need a 68-pin external cable, then I can pretty much use
   any cable as long as the pins are all connected and the
   total bus length is okay--so a 1ft. cable labeled "differential"
   will work just fine with FW/SE or with LVD in addition to
   the HVD it was probably intended for.
 - When termination (internal or external) gets involved, then
   *sometimes* a "perfect" terminator (or an "active" terminator
   which somehow isn't quite the same thing) will work with
   any type of setup--but pretty much if you're working with
   HVD gear then you want HVD terminators.
 - Although "Ultra160-rated" cables might have some fancy
   braiding or shielding to help with RFI at the higher speeds,
   they'll work fine at lower speeds--and in general plain old
   FW SCSI-2 SE cables will work fine too.

Any gurus out there want to educate me on problems with
the above?  The biggest thing I'm trying to figure out is when
HVD terms are *needed*, and (separately) when they are
*acceptable*.  And what's the *real* difference between an
active terminator, a passive terminator, and a forced perfect
terminator?  (If there's a good reference that tells me all this
then just point it out--I've checked through a bunch of stuff
online without finding clear answers...)

  --Rip