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From: walk@mrcnext.cso.uiuc.edu (Todd Walk)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: super high density formatters
Message-ID: <1990Nov20.193242.10686@ux1.cso.uiuc.edu>
Date: 20 Nov 90 19:32:42 GMT
References: <1990Nov16.035524.22022@ux1.cso.uiuc.edu>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
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ftw33616@uxa.cso.uiuc.edu (Frank T. Wang) writes:


>has anyoe used those programs that can format a 1.44 meg disk to, say, 1.7 meg?
> and other such HIGH formats?  how unreliable are these?  i figured it'd be
>as dangerous as formatting a DD disk HD.

>					Frank


All programs for the IBM that do this add 1 extra sector per track (or 2 or 3..)At 1 extra sector per track, a 720K IBM disk (9 sec., 80 tracks) is increased
to 800K (about the most 1MB unformated disks can hold while formated).
With a 1.44MB disk you can squeeze on 2 or 3 extra sectors per track, giving	between 1.6-1.8MB.  As for the reliability of adding these extra sectors to the
tracks, that depends on the individual diskettes.  A value called the          
coercitivity determines the magnetic strength of the disk and is very important
in determining how much information can be put on it.  For 1MB 3.5" disks it
is about 600, 2MB 3.5" about 700.  The amount of coercitivity that a disk
actually has is a factor of the manufacturing process and can vary              significantly.  If it is lower than it is supose to be, the disk will be    
unreliable with the extra sectors.  Plus, old disks tend to lose their
coercitivity.

As for why you can't get 1MB of storage on a 1MB unformated disk       
(and 2MB on a 2MB...), disk manufacturers measure the amount of bytes that
can be reliably placed on the disk (of course you can get more bytes on the 
outside tracks than on the inside tracks).  Therefore, with a constant speed
disk drive (such as the ones on IBMs), you get much less than the unformated
density.

						Todd Walk
						walk@mrcnext.cso.uiuc.edu