prindle@NADC.ARPA (Frank Prindle) (06/29/89)
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
fred@cbmvax.UUCP (Fred Bowen) (06/30/89)
In article <POSTNEWS6463@NADC.ARPA> prindle@NADC.ARPA (Frank Prindle) writes: >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. Interesting. I have warned folks in the past about using paper-type write-protect tabs, which can have the same effect. Also, I often find myself working on disk drives with the top case cover removed (imagine that :-). It was not until I wasted a day or two chasing after problems that I discovered the sunlight was effectively "shorting" the write- protect and disk-present photo sensors. And all along I thought I just naturally worked better at night. -- Fred Bowen uucp: {uunet|rutgers|pyramid}!cbmvax!fred arpa: cbmvax!fred@uunet.uu.net tele: 215 431-9100 Commodore Electronics, Ltd., 1200 Wilson Drive, West Chester, PA, 19380