From: Jim Stewart <jstewart AT owlnet DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: The is world dropping MS-DOS.  What about DJGPP? (Was Re: Quake
Date: Fri, 12 Sep 1997 15:34:18 -0500
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Paul Derbyshire wrote:
> Just out of curiosity... I hear here all the time about the FAT.
> "Brain-damaged FAT"... "shortcomings of FAT"...etc. As I understand it the
> FAT serves a becessary function, tracking which disk blocks are free and
> which are not. It uses a bit for every block on a disk. As far as I
> understand it, the only real problem is it takes up a fair bit of space.

> One thing I can think of with perfect compression would be linked lists...

It's very probable that nobody cares, but:

The FAT actually is a linked list.  IIRC, there is a n-bit cell (12 bits
in oldest DOS, 16 in somewhat newer, dunno now) in the FAT for each
cluster on the disk.  That's what scandisk is talking about when it
means chains.   Each directory entry points to the head of the FAT list
for that file.  Each entry in the fat is a pointer to the next entry or
an FFFF (or some such) for the end of the list.  You get the position on
the disk for that cluster by the position in the FAT.

Deleted files are recoverable because the only thing that happens to
delete a file is the first character of the name of the file gets
stomped in the directory entry.

I'm not sure how free blocks are maintained or found or such.

Jim