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From: Charles.E.Dubuque@dartmouth.edu (Charles E. Dubuque)
Newsgroups: comp.sys.mac.system
Subject: Re: HD disks failing at 800K format
Message-ID: <1991Apr10.160835.5153@dartvax.dartmouth.edu>
Date: 10 Apr 91 16:08:35 GMT
References: <56990001@hpindwa.cup.hp.com>
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Organization: Dartmouth College, Hanover, NH
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Using high density disks in an 800K drive is not like using Chrome
cassette tapes in a tape deck meant for regular cassettes (which works
fine but gives none of the advantages of Chrome). HD disks simply
CANNOT be used as reliable 800K disks. I believe the problem is
two-fold. 

Since HD disks have to store about 2 times as much information in the
same surface area, I would imagine that: 1) the HD drive writes a
signal that is of lesser strength than an 800K disk, otherwise it would
destroy data. 2) that the HD disks are of a more sensitive medium than
800K disks, since it needs that extra sensitivity to pick up the weaker
signal.

Now, put a piece of Scotch tape over the HD disk and format it in a
dumb 800K drive. It seems to work fine, but everytime you write, things
start to get erased and overwritten, or mis-written or misread because
(1) the 800K drive is writing a stronger signal to a more sensitive
medium (2) the 800K drive is looking for a strong signal from a weaker
signal medium.

All this adds up to the problems you describe.

Moral of the story: never use HD disks in 800K drives. It isn't meant
to work that way (notice that Apple doesn't give you the option of
formatting HD disks ar 400K,800K or 1.4M)

Chuck
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Chuck Dubuque           ||"It's one thing to think something that seems
Dartmouth College       || completely impossible. But quite another to
HB 4233 Hanover NH      || say it..." -- Silent Invasion, book II
03755                   || 
C.Dubuque@Dartmouth.edu || DartmouthUs -not- the Review, but it's close
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