Real tape drive densities

Jay Jaeger cube1 at
Sun Feb 14 16:08:46 CST 2016

On 2/13/2016 6:33 AM, Christian Corti wrote:
> On Thu, 11 Feb 2016, Christian Corti wrote:
>> I have a 7970B (-236) with options 127, 006, 007, 012 and 023.
> According to the HP 1000 Peripherals Selection Guide from 1982, page 16,
> option 236 specifies an 800bpi master magnetic tape subsystem with one
> drive and two-card 13181B interface.
> And you can't mix 800 and 1600 bpi on the same interface for the HP
> 1000. You need either the 13181 for NRZI, or the 13183 for PE.

That makes sense: different formatters would be required.

> So, apparently my NRZI 9 track drive has the density option included,
> and I don't know if there were any other 200/556 bpi 9 track drives out
> there. When we got the drive I had hoped it would be a 7 track drive,
> but it isn't.
> Christian

I have never heard of 200bpi or 556bpi for anything other than 7 track.
I cannot imagine why anyone would ever produce such a thing.  The only
density I have ever heard of as being available on both 7 track and 9
track is 800BPI NRZI, from any manufacturer, and I have seen quite a lot
of them over the years.  Nor have I ever seen a 9 track tape whose label
on the exterior claimed it had been written at 200 BPI or 556 BPI.

Your S/N has prefix 1124, so it looks like this manual is applicable:

Looking at this manual for the 7970B / 7970E I see that dual 7/9 track
heads did exist.  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
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.

The buttons clearly imply a NRZI drive (rather than 1600 BPI PE).


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