720k 5.25 disks

[uhclem at trsvax.UUCP]

<>
B>I have an ATT (Olivetti) 6310 AT clone running SCO Xenix/MSDOS 3.3. It
B>has one 1.2 meg drive. I regularly format 5.25 disks to 720 K. These
B>disks work fine under both Xenix and MSDOS on the ATT whether used with
B>tar (linear sector addressing) or MSDOS directories.

B>When I try to transfer these disks to a 286 Zenith (also running MSDOS
B>3.3), I encounter various problems. With MSDOS directory disks, the dir
B>command (also ls under MKS) will list all the files on the disk but
B>copies and reads fail. With tar disks, sector reads (using int 13) fail
B>after the first track. The absread and biosdisk functions (TURBO C)
B>also fail.

Although this does not answer the question you asked, it may eliminate the
question.  Your Zenith system may be like some other MS-DOS systems whose BIOS
can't cope with the idea of 5.25 == 720K.  They assume 5.25 == 1.2  or 360K.
This is partly because IBM limited what configurations you can have in CMOS,
and they never sold a 5.25" 720 drive.

The fact that only the directory can be read (cylinder 0) is a clue that
the operating system thinks cylinder 1-n are elsewhere.  You are probably
getting seek errors, although DOS probably won't report it as such.

It is extremely unlikely that the media density was ok to handle the format
on cylinder 0 but never works on cylinder 1 or higher, although you should
be using 80Tk 96TPI media for 720K operation.

If you can watch the heads while it operates, stick one of these disks in
and seek about two-thirds into the capacity (720K remember) and see if the
head pegs out on the inner stop.  You may even be able to hear it.
Don't worry (TM).  The IBM startup test does this every time you boot,
which most clones copied even though it is not very good for the drives.
If it does peg, then the system is treating the drive as a 1.2 meg reading
a 360K and is double stepping the head for each cylinder increment.
(Under XENIX, pull out your uPC765 manual and decode the status returned
 in the read error.  If it is a seek error, this is what you have got.)

I routinely have to transport data to an older system with 5.25 720K drives
and my MS-DOS system steadfastly refuses to cooperate.

To get around this, I lie to the CMOS and tell the system that the drive is
a 3.5" lowcap, which holds 720K.  The BIOS quits double-stepping and I get
my files across the abyss.  Don't forget to put the CMOS back when you are
done.  Under XENIX, you should be able to force recognition by using the
appropriate dev, that is if the XENIX floppy driver was written properly.
I haven't tried this with the "real" SCO XENIX floppy driver.

Hope this helps.


<This information is provided by an individual and is not nor should be
 construed  as  being  provided  by  Radio  Shack or Tandy Corp.  Radio
 Shack/Tandy Corp has no obligation to support the information provided
 in  any way.>
						
					"Thank you, Uh Clem."
					Frank Durda IV @ <trsvax!uhclem>
				...decvax!microsoft!trsvax!uhclem
				...sys1!hal6000!trsvax!uhclem