Real tape drive densities

[Christian Corti]

On Sun, 14 Feb 2016, Jay Jaeger wrote:
> Looking at this manual for the 7970B / 7970E I see that dual 7/9 track
> heads did exist.

Yes, but only in read-only configurations.

> Yours has a plate that claims it has option 127 (as
> well as 6, 7, 12 and 23).   The 127 implies a 9 track only head, but I
> suggest you pull the head cover off to see if you can find a part
> number.  What the plate claims, and what the machine actually is can

I've added another picture of a closeup of the R/W head. In my opinion 
it's a 9 track read-after-write head. The geometry and gaps are identical 
to those of the adjacent 7970B 800bpi-only tape drive we have.

> differ for all sorts of reasons.  And the sticker is coming off at the
> edges as well - it may have been *moved* from one frame to another.
> Wouldn't be the first time - particularly in a university setting.

I think it's the original sticker, the options listed on the manual 
(hand-written by HP on the cover page) match, and the date codes (1971) 
match, too.

Christian