3B1 and 60386 floppies

[Peter Fales]

In article <2986 at cbnewsc.ATT.COM>, psfales at cbnewsc.ATT.COM (Peter Fales) writes:
> 
> It is slightly more difficult to go the other way, because 
> you have to make sure that there is a VHB on the 3b1 disk.  One 
> way is to format on the 3b1, then write the disk on the 6386, 
> finally reading it back in on the 3b1.  Alternatively, you can
> keep on copy of the 3b1 boot track on the 6386 and write it out
> when necessary.

It has been pointed out to me that I forgot to mention the warnings
about interchanging disks between 40 and 80 track disk drives.  In
particular my comment about formatting on the 3b1, writing on the
6386, and reading on the 3b1 is risky (though it may work).

The rules are these:

- 40 track drives have wide heads.  80 track drives have narrow heads.

- Anything written with a wide head can be read (with high confidence)
	by either a narrow or a wide head.
	
- Anything written by a narrow head on a new (out of the box) or
	bulk-erased disk can likely be read by either a wide or
	narrow head.
	
- Anything written by a narrow head down the middle of a wide track
	previously written on a 40 track drive can likely be read
	by the narrow head.  But if read on a 40 track drive, the
	head will pick up both the original data and the new data
	written down the middle.  This may cause problems, though
	in practice you can sometimes get away with it.
	
Summary:  If you are just trying to transfer data from machine to
	another, and the data on the floppy is not critical you
	may not need to worry.  If your only copy of the data is
	on the floppy, writing on both 40 and 80 track drives 
	is risky at best.
-- 
Peter Fales			AT&T, Room 5B-420
				2000 N. Naperville Rd.
UUCP:	...att!peter.fales	Naperville, IL 60566
Domain: peter.fales at att.com	work:	(312) 979-8031