3b1 floppy tape project (still on back burner)

[Bill Mayhew]

Hi,

A while back I mentioned that I was planning to look into the
feasibility of using one of the low cost floppytape drives as a
backup device for the Unix PC.  Basically a floppytape drive
attaches to an interface cable that would normally connect to a
standard 5-1/4 inch disk drive.  One could replace the original
5-1/4 Teac 55B drive of the 3b1 with a tape drive.  What makes this
intersting is that the cost of the tape drives is as low as $350.

I talked to Walt Mazeur at Archive Corp. which makes drives.  He is
in their data systems division.  He has been involved in writing
software drives for various systems.  One limitation he pointed out
is that with current generation floppytape drives are not capable
of operating in an interrupt driven mode.  Basically, the CPU has
to busy wait for the drive to finish a given operation.  In 4 to 6
months, drives will be available that can generate interrupts when
a tape operation has completed.  Capacities up to 80 megs will be
available that can still fit into a 1/2 height 5-1/4 cutout.

Apparently Archive has been working with SCO on writing drivers for
Xenix.  He estimated that about 3 person-months of time would be
needed write a fully debugged Unix driver.

It looks like the current generation of floppytape drives might be
workable, if you went to single-user run level so that you could be
sure that nothing was going to clobber your timing.  That sounds
like a good idea anyway, as you wouldn't want some joker writing to
a file that was being backed up.

In short, the floppytape units are quite a bit different from a
floppy drive to the extent that software that a floppytape appears
invisible to software that is looking for a floppy disk -- so that
an tape in the drive doesn't accidentally get munged by errant
floppy writes.  The electrical signals are similar enough that a
standard floppy drive controller chip can be conned into generating
them.  Basically the trick to waking up the tape is to send it a
sequnce of pulses on the head select and step leads.  Exactly what
the commands are, I don't have at hand yet.

Any comments from netland are invited.


--Bill