14 Feb
2016
14 Feb
'16
7:41 p.m.
On 02/14/2016 05:36 PM, Chuck Guzis wrote:
On 02/14/2016 02:08 PM, Jay Jaeger wrote:
Well, that could be a malfunction. Some tape
drive-formatter sets cannot do this without hardware
problems. But, some had software-controlled density, and so
the software could override the detected density when the
tape was mounted. 800 NRZI had nothing recorded over the
BOT marker, 1600 and 6250 had distinct patterns written over
the BOT marker to ID the density. Once the density is
identified, it SHOULDN'T allow you to change it in the
middle of the tape.
Jon
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.