Date   : Thu, 24 Oct 1991 06:45:03 -0700
From   : Sprague.Wbst311@xerox.com
Subject: Re: general (Floppy Drives on the Xerox 820-II)

And I have to disagree with some of Erik Lindbergs comments.  :-)

> I have seen drives that tested "ready" by looking for index timing,
> that wouldn't ever come "ready" if you used a hard sectored diskette
> in them.

The drives or BIOS?  It's true that what you said is *PART* of how the 8" and
5.25" High Density drives test for drive ready (assuming that the 5.25" HD
drives even has the Drive Ready option), but note that most 5.25" do not even
HAVE the signal (I have never seen one that does).  However, a BIOS that tests
for the drive being ready be testing the index hole timing is the BEST type of
BIOS for substituting 5.25" HD drives for 8" drives!!!  :-)

> Many of the lower cost floppy drives manufactured now have no
> jumpers to configure device select, motor control, etc.  In other
> words, it will work only if it is OK with you that all drives are
> selected with DS1 and are configured for "select with MOTOR ON".

Hmmm, I have seen this trend in 5.25" High Density floppy drives, but not on
the typical "360K" drive.  On High Density drives there are usually two jumpers
to select DS0 and DS1, instead of four jumpers.  I have never seen one with no
jumpers, though that does not mean they don't exist.  In addition, your correct
in saying there is usually no way to configure MOTOR ON to work with Drive
Select.

I have yet to see a "low density" drive with less than four drive selector
jumpers (does not mean they don't exist though).  In addition, there is
*usually* a way to configure MOTOR ON to be driven by DRIVE SELECT, though you
might have to look for it.  I have a pair of Chinon "low density" drives (you
wanna talk about cheap drives), and by following the MOTOR ON trace, I quickly
found where I needed to solder a jumper between two pads to tie MOTOR ON to
DRIVE SELECT.  While these drives did not provide jumper pins, the ability was
still there.

In any case, many non-PC 5.25" controllers already have a MOTOR ON signal,
unless the controller is meant to drive both 5.25" and 8" drives.  Even then
though, it still might have a MOTOR ON signal.

> Then there is the matter of the 5.25" HD floppies, which DON'T have
> "exactly" the same interface as a Kaypro,

The interface differences are so little that they should not matter, unless the
Kaypro did something *VERY* non-standard.  The signal pins that the Kaypro
should actually be using are pin-for-pin identical!  There are different
reasons that the HD drives do not "plug-n-play", but it's not because of the
hardware signal interface.

BTW: The differences on the HD drives are pin 2, SPEED SELECT, and Pin 34 DRIVE
READY/DISK CHANGE.  There are "no connection" pins on the "low density" drives.

> and nobody had ever heard of them before
> they appeared on the IBM AT.

Again, not true!  They had been around for several years before the IBM AT used
them.  It's just that they were never POPULAR (read inexpensive) until the AT
used them.  They were developed to replace the 8" drive, but by the time they
got to market, the 8" drive was already dead, and everyone was using the 5.25"
"mini-floppy" drives.

> I would argue that those [High Density Drives] would also be
> called "IBM PC floppy drives".

Feel free, but I am not sure why you would want to.  I have a pair of them
running on a Xerox 820-II.  Fuji Xerox used them in their workstations (which,
by the way, are older than the IBM AT), and I have seen them in other non-PC
computers.  Personally, I would NEVER call a floppy drive an "IBM PC floppy
drive" unless it ONLY worked in a PC and nothing else.  :-)  I know of no
drives like that.

                               ~ Mike  (Sprague.Wbst311@Xerox.Com)