Real tape drive densities [was RE: Oregon Pascal tape found]

[Brent Hilpert]

On 2016-Feb-10, at 3:37 PM, Rich Alderson wrote:
> From: Curious Marc
> Sent: Wednesday, February 10, 2016 12:05 PM
> 
> Top-posting,
> 
>>> On Feb 10, 2016, at 11:40 AM, Rich Alderson <RichA at LivingComputerMuseum.org>
>>> wrote:
> 
>>> From: Christian Corti
>>> Sent: Wednesday, February 10, 2016 2:28 AM
> 
>>>> I actually *do* have a 9 track tape drive (HP 7970) that has 200/556/800 
>>>> bpi densities:
> 
>>>> http://computermuseum.informatik.uni-stuttgart.de/pics/hp1000/hp7970_2.jpg
> 
>>>> And it is a *9* track tape, I know for sure.
> 
>>> Actually, what you have is a *dual-density* tape drive, an HP7970E.  It
>>> will write 9-track tapes at 800bpi, or 7-track tapes at 200, 556, or 800.
> 
>> Nice unit! Drool. Looks like this is a NRZI triple density tape, so
>> 7970A or B. The later 7970E would have a 1600 PE density switch too. I
>> have an E, but not with the multiple density or 7 track options
>> unfortunately. Thanks for the link to the series overview manual Rich.
> 
> Note that Christian Corti stated that his drive is capable of 9-track
> operation.  That's an E.  (Apparently that will also write 9-track PE at
> 1600bpi, but it will write 9-track NRZI at 800bpi).

Not sure whether you're intending a qualifier to the 9-track  /  E model association,
but 9-track drives in the 7970 series go back to the 7970A (I have a 7970A in the 9-track, 800BPI variant).

The HP 7970 B/E manual shows only 3 model-options with 200 & 556 bpi:

	- 7970B-136   200/556/800 7-track

	- 7970E-164   200/556/800/1600, dual-capability 7 & 9 track, READ-ONLY
	- 7970E-165   200/556/800/1600, dual-capability 7 & 9 track, READ-ONLY

None of the dual-capability 7 & 9 track model-options listed in the manual are capable of writing, nor is any model-option listed capable of writing 200/556 9-track.
An HP manual speaks of HP producing dual-capability 7&9 track heads but they are read-only heads.

Photos in the manual show the dual-capability 7&9 variant with selector switches for 7&9 track and 1600 bpi (in addition to the 200/556/800 selectors).
The unit presented by Christian does not have the additional selectors.

The manual does mention that there are non-standard, "Special" variants.
The manual mentions 7970C as a 'special configuration' of the B but doesn't say what the difference is.

If the unit presented by Christian is 9-track, it does not seem to be any of the standard B or E variants.
I'd suggest resolution would require Christian to identify the model & option (specific model label is on the inside in my unit).