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From: fischer-michael@YALE.ARPA.UUCP
Newsgroups: comp.sys.atari.st
Subject: Lost disk sectors
Message-ID: <8707071803.AA02575@yale-eli.arpa>
Date: Tue, 7-Jul-87 14:03:57 EDT
Article-I.D.: yale-eli.8707071803.AA02575
Posted: Tue Jul  7 14:03:57 1987
Date-Received: Thu, 9-Jul-87 06:31:44 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
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I wrote a little program to display the FAT (File Allocation Table)
on a disk that appeared to be completely full and was surprised
to see the last two clusters (= 4 sectors) free.  Looking at the
data itself confirmed that they were unused.  Doing a little
arithmetic, I came up with the following: When formatting a SS disk,
TOS announces 357376 bytes free.  Floppy disk space is allocated
in clusters of 2 sectors = 1024 bytes, so 357376 bytes = 349 clusters
= 698 sectors.  Add to that 1 for the boot sector, 5 for each of
the 2 copies of the FAT, and 7 for the root directory, and you get
a total of 716 sectors.  A standard format disk has 80 tracks times
9 sectors per track for a total of 720 sectors, so indeed there is
a discrepency of 4.  Similar results apply to a DS disk:  TOS
announces 726016 bytes free = 709 clusters = 1418 sectors.  Add
to it the 18 sectors at the beginning to get 1436 sectors, 4 less
that the 1440 on a raw disk.

Has anybody else noticed this before?  Is it a TOS bug?  If so,
has it been fixed in the newer ROMs?

--Mike Fischer 
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