Date   : Mon, 21 Oct 1991 07:40:41 GMT
From   : ogicse!milton!sumax!polari!rwing!fnx!del@uunet.uu.net (Dag Erik Lindberg)
Subject: Re: general (Floppy Drives on the Xerox 820-II)

Sorry, Ian, but I just gotta disagree with you on a few of the points
that you are so vocally "correct" about.

In article <Niqu02w164w@ijpc.UUCP> ianj@ijpc.UUCP (Ian Justman) writes:
>ritchie@hpdmd48.boi.hp.com (David Ritchie) writes:
>
>>   I think that these are probably hard sector drives, so the answer is
>> 'no'. 
>
>Wrong, pal.  There's no such thing as a "hard-sectored drive" in
>the 5 1/4" world.  Besides, ALL  FM and MFM soft-secotred setups
>have and use the said emitter-dectector pair.  Even the IBM PCs

True, all drives use the emitter-detector pair.  Wrong, there is
such a thing as a "hard-sectored drive" in the 5 1/4" world.

>use them. That's how the hardware finds sector 1 on each track.
>In the world of soft-sectors, it's called the "index detector";
>in hard sectors, it demarcates each sector and says where the
>track starts/ends.

Exactly, and that is the difference.  For the "hard-sectored drive"
the drive had on-board logic to determine where the start of the track
was, and provided *TWO* index outputs on the interface connector.
One index output indicated the sector pulses, one indicated start of
track.  This is not to say that most standard drives won't work with
hard sectored disks, given the right controller.  BUT, 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.

>BTW, there's no such thing an an "IBM PC floppy drive".  There
>ain't no such thing.  The interface is exactly the same as if you
>had taken your disk drive from your Kaypro and plugged it into
>your PC.

While it is true that the interface for an "IBM PC floppy drive" is
exactly the same as other 5 1/4" drives (assuming DSDD), there is one
significant difference.  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".
These I would certainly call "IBM PC floppy drives", since if I was
designing a system, or using it in an old Kaypro, those are not the
interface configuration options I would select.  Then there is the
matter of the 5.25" HD floppies, which DON'T have "exactly" the same
interface as a Kaypro, and nobody had ever heard of them before they
appeared on the IBM AT.  I would argue that those would also be called
"IBM PC floppy drives".


-- 
del AKA Erik Lindberg                             uunet!pilchuck!fnx!del
                          Who is John Galt?