[TUHS] Choice of Tape Format for BTL UNIX Distro

[segaloco via TUHS]

Surprise surprise, another hyper-specific topic incoming.  I am curious
if anyone on-list can provide insight on this topic.  Setting Up Unix -
Seventh Edition indicates:

> The tape is 9-track 800 BPI...

Was this a matter of convention given the general computing ecosystem at
the time, or was this more driven by Bell System standards for magtape?

I find myself curious as I recently procured a 7-track 556 BPI transport
which, while not applicable to V7 UNIX tapes as so described, has me
itching to explore the world of magtape further, including eventually
tracking down a 9-track supporting the necessary BPI should another UNIX
tape needing preservation surface.

I also recently got a QIC drive (not the right size for the early 90s
BTL tapes I have) and am exploring repurposing the read head to yank
data off these janky QIC tapes I have.  Needless to say, magnetic tape
media and preservation is on the mind lately.

Further on the subject of UNIX tapes though, was there any regular
shipment of other media not matching this description or was it pretty
settled that

order_unix()

has a return type of

mt_track_9_bpi_800_t

?

- Matt G.