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From: prindle@NADC.ARPA (Frank Prindle)
Newsgroups: comp.sys.cbm
Subject: Colored diskettes - write protection warning
Message-ID: <POSTNEWS6463@NADC.ARPA>
Date: 29 Jun 89 12:29:28 GMT
Sender: prindle@NADC.ARPA (Frank Prindle)
Lines: 22

I found yesterday, quite to my astonishment, that the infrared LED/photo-
transistor sensors used in some disk drives can "see right through" color
diskette shells such as those used by Sentinel color diskettes. I found
that I could put such color diskettes into two of my drives upside down
and format and write to the back sides WITHOUT punching a notch! This
applied to every color - red, blue, green, yellow, orange, purple, etc... not
just the light ones! Yet black shell diskettes would always lock out
writing ok. This does not apply to the 1541/1571 family (at least not the
ones I have), but is definitely happening on some 1541 clones. I assume
that the composition of the plastic is such that it is semi-transparent to
infrared light, and the drives in question are overly sensitive to the small
amount that leaks through.

The warning, therefore, concerns commercial software distributed on color
diskettes with no notch present in the disk. It may not be safe to assume
that it is impossible to accidentally write on the disk! It is easy enough
to test your drive(s) for this condition - just try to format the back side
of an empty color diskette without punching a hole.

Sincerely,
Frank Prindle
Prindle@NADC.arpa