There is some interesting info at the hp.com site at
http://www.hp.com/tape/c_switch.html

Bob Thelen
Sherlock Support Group

Dirickson Steve wrote:

> >  I was told by HP that as long as compression is turned off and I do not
> > use a tape
> > length that is invalid, I can create a tape to be read on a
> > customers 2gb
> > dds dat drive (dds1 or dds2).
> >
> > Is this info correct?
>
> Yes; subject to the vagaries of misaligned heads and other
> mechanism-specific problems, any tape written to the DDS or DDS-2 spec can
> be read by any other drive capable of reading that format. Just like QIC, or
> cassette tapes.
>
> > Do you turn off the compression thru software or a hardware jumper?
>
> Yes ;-)
>
> The drives are normally set to allow software control of compression by the
> host. If you want to, you can open up the case and change the settings on
> the DIP switch (well, at least the C1533 mechanism has it on the bottom of
> the mech). Many moons ago I had (and posted to the list) a description of
> what each switch position does, but I don't seem to be able to find it at
> the moment. Perhaps it's in the list archives. As an alternative, the
> information at
>   http://www.hp.com/isgsupport/pictures/t_rear.gif
>
> may be of interest/value. It seems to indicate that setting position 2 of
> the DIP switch to OFF permanently disables compression.
>
> Steve