> It is.  The zip drive actually has two DB25s on it, one "in" and one "out".

Right.  Some of LaCie's drives came like this, too.

> > and you'll find an appropriate adapter cable at any Macintosh shop
> Hardly.  The drive comes with a cable designed to connect it to a
> Macintosh; it's male DB25 on each end, but is _not_ symmetric: flip the
> cable end-to-end and it won't work.

I don't know why the 25-25 cable isn't symmetric (if you discovered that by
experiment rather than documentation, that cable may be defective).  However,
if you want to attach this drive to a standard SCSI connector, AMP part number
556297-1 and similar, then the usual "Macintosh system cable", DB25-to-
Centronics-50, is precisely what you want (or so I've been told).

HMM.  Unless Iomega decided to screw their customers by not using Apple's
pinout, but choosing their own.  But I've read on the PC newsgroups that
the standard Mac cable works.

I just checked Iomega's web page (http://www.iomega.com/, natch).  They are
astonishingly nonspecific about cabling requirements.  And they don't supply
a customer support address, either.  Thanks, guys.

> > (unless, it turns out, you own a Macintosh, in which case you need a
> > fairly rare DB25-to-DB25 *SCSI* cable; note that a 25-wire serial
> > cable *won't* do).
> Why not?

A SCSI cable needs 50 wires, in 25 pairs (well, 23 pairs I think), because
each signal line MUST be a 100-ohm TRANSMISSION LINE, not just a wire.  If
you put SCSI signals on something other than a 100-ohm transmission line, you
WILL get reflections which can distort the signals and corrupt data, just
like when you don't use terminators.  The 25 pin connector introduces a
small impedance bump, but fortunately not a fatal one (the severity of
reflections is a product of both the impedance difference and the length of
the impedance mismatch).

> Except what I need is a cable to connect it to a (so-called) DB-50.
> Not a Centronics-50.
> 
A DB-50?  You mean something that looks like a stretch DB-25, with pins
and everything?  What the hell uses that?  (Or is this a Sun, with that
tiny mutant three-row connector?)

> What I know works: the iomega-provided cable, to a DB25 F-F
> gender-bender designed for RS232 (this is why I ask why serial 25-wire
> cables won't do),

The gender-bender introduces a 2" long impedance bump, PROBABLY short enough
that you're not experiencing major reflections.  Use two feet of random wires,
and it will ring like a bell choir.

I've *heard* of Mac-system-to-micro-SCSI cables, but none of my catalogs show
them.  (And there seems to be at least some possibility that the Iomega
connector is a bizarre pinout.  Well, more bizarre than Apple's, anyway.)
But you need to make sure that you maintain transmission line characteristics
on your cable (if you value your data, anyway), so you may need to rip open
that 25-25 cable to figure out which line is ground, so that you can ground
all the transmission line return wires properly.  (Of course, you might open
that cable and find that it really is just 25 wires, in which case you've
learned how Iomega made such an inexpensive package, and have been given a
clue what the hidden cost of the drive is -- reliability).

> We've found a shop that is willing to do custom cables, and are
> having them wire up an appropriate cable, based on handing them the
> above mess and saying "here's your reference for the wiring".

Make sure they understand how to wire *SCSI* cables, as transmission lines,
or you will likely come to grief.