Real tape drive densities

Chuck Guzis cclist at
Sun Feb 14 17:36:28 CST 2016

On 02/14/2016 02:08 PM, Jay Jaeger wrote:

> 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.

That would agree with my own experience as well.  800 NRZI and 1600 PE; 
6250 GCR.    There may have been non-computer (e.g. data logging) drives 
in 9-track with lower densities, but I've not run into any.

Some drives apparently *can* mix densities.  I came across an AT&T 
distro tape recently for SVR4 that started with 6250 GCR and then after 
the first tapemark, switched to 1600 PE for the remainder of the tape. 
I managed to read it in two passes--the first is the drive set to 6250 
at loadpoint, then with the drive set to 1600 at loadpoint.   All data 
was complete, so it's a puzzlement.


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