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From: phys169@canterbury.ac.nz
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: First sector of the file area
Message-ID: <1990Jul20.120532.8741@canterbury.ac.nz>
Date: 20 Jul 90 12:00:02 GMT
References: <29744@eerie.acsu.Buffalo.EDU> <3050@rwthinf.UUCP>
Organization: University of Canterbury
Lines: 25

In article <3050@rwthinf.UUCP>, berg@cip-s03.informatik.rwth-aachen.de
 (Solitair) and others write:
>>>.. Anybody know how I can find out
>>>the sectore number of the first sector of the file area of a hard disk

>>On a 20 meg hard disk, the FAT of the root directory should be at sector 83.

> The way to follow is this: Read the partition sector on the hard-disk,

The best way is to avoid the calculation, since DOS ignores some of the
parameters in that first sector, and different versions ignore it in different
ways, putting the first sector in different places. It's better to have your
TSR program get DOS to do the work, by either doing the work inside an int 28h
routine, when it is safe to use most modern DOS calls (e.g. set a flag in your
keyboard interrupt handler, which your 28h handler looks at), and/or intercept 
int 21h and avoid conflicts by checking for work to be done after calling the 
original int 21h has been called.

Second-best is to use int 25h after checking do disk activity is in progress;
this is still pretty safe, still works with many networks (e.g. Decnet Dos, but
NOT Novell), and lets your TSR get a slice of the action a little more often
than the super-safe method above.  You shouldn't need to look at partition
information unless you want some extra-efficient print spooler or such like.

Mark Aitchison, Physics, University of Canterbury, New Zealand, Up Under.