Strange magtape anecdote

Guy Sotomayor ggs at
Tue Oct 27 01:24:58 CDT 2020

We had a similar problem when I was at IBM and we were developing a
follow on to the PC/AT (it never shipped).  We had a bunch of
prototypes in the lab running tests with stepper HDDs (rather than
voice coils)  We kept having disk errors (failure to find track 0) when
running tests.

It took us a while to figure several things out:
1) all of the machines were run with their covers off
2) all of the machines that failed were by the windows
3) the failures always happened at a particular time of day

After a bit of head scratching we discovered that the tack 0 sensor was
optical and at that particular time of day the sun at a particular
angle did not allow the sensor to register that the drive was at track

TTFN - Guy

On Tue, 2020-10-27 at 06:50 +0100, nico de jong via cctalk wrote:
> Hi all,
> Back in the early 70's I was an operator on an IBM 360/40 with 4 
> tapedrives. Nobody could understand that sometimes a tape transfer
> would 
> stop saying "end of tape", mainly around 3 PM, when not called for.
> It 
> was mainly one specific drive, but its two neighbours, one on each
> side, 
> could also behave like this. Tape drive specialists visitied us, 
> scratched their heads, and went off again. When the blinds were
> rolled 
> down, the error disappeared. The reason for the strange behaviour
> was 
> that the sun could shine into the machine room when it was in a
> specific 
> position, so it could send some light into the drive, where the tape 
> then reflected the light into the sensor, making it believe that it
> had 
> met the end-of-tape marker.
> /Nico OZ 1 BMC
> On 2020-10-26 17:01, Al Kossow via cctalk wrote:
> > 
> >
> > 
> > "George Dragner always wore a belt with a metal dragon buckle.  He
> > was 
> > a colorful character known for pissing off management.  His most 
> > famous act was tossing a chair through the window at a customer
> > site. 
> > The customer refused to believe that the lack of humidity in the
> > room 
> > was screwing up his magnetic tape media.  As the tape heads depend
> > on 
> > the moisture from the air to prevent the magnetic oxide from being 
> > torn off the media from the friction during a rewind. George broke
> > the 
> > window to prove his point.  He was right ! "
> > 
> > There is a minimum RH specified for tape, but "tape heads depend
> > on 
> > the moisture from the air"  ??
> > 

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