rbr@bonnie.ATT.COM (4197,ATTT) (12/01/89)
This question sure has been around a long time. First it was the APPLE II
folks that hit on the idea to double capacity by adding another write-protect
notch on the other edge of the disk. Then came double density foppies and
eveyone was formatting cheaper single density disks at double density.
I would like to add my experience to the compendium of information on this
rather worn out topic. I had (and still have) a TRS-80 III with two 740-K
floppy drives. When I first installed these drives, DS/QD (96-tpi) 5 1/4"
floppy disk sold for $4.50+ each. When I discovered, quite by accident,
that I could format $1.29 DS/DD diskettes at 740-K, I rushed out and bought
a bunch of DS/DD diskettes. Sure enough, 9 out of 10 would format just
fine. However, a year later, I began to get read errors. Usually I could
fix the error using SUPERZAP that came with NEWDOS 80, but not always.
While attending a Southeastern Regional Computer Measurements Group meeting,
I got into a conversation with a technical manager of a company that
manufactures magnetic media. He stated that the design of a diskette began
with the design or selection of the magnetic media which is selected for
a density much greater than the intended density to allow for substantial
variations in the manufacturing process. Therefore it is possible to use
diskettes at higher densities (maybe). Also he allowed, after much prodding,
that when they manufactor high density dikettes, they test them at the upper
limit of the high density range. If they fail, they are tested at a lower
density. If only one side failed, they were labled single sided. Later,
I confirmed this with a freind who works at another company that manufactures
diskettes.
I presume that the same is true with 3 1/2" diskettes.
The moral is: Don't put anything critical on 720K disks formatted at
1.44M and expect to read it six months from now.
Robert B. Rager
AT&T Federal Systems att!bonnie!rbr
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