Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!cbfsb!cbnewsc!tjr
From: tjr@cbnewsc.att.com (thomas.j.roberts)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Turbo-C 2.0 absread() / abswrite()
Message-ID: <1990Nov30.183106.29270@cbnewsc.att.com>
Date: 30 Nov 90 18:31:06 GMT
References: <valley.659978709@gsbsun>
Organization: AT&T Bell Laboratories
Lines: 23

From article <valley.659978709@gsbsun>, by valley@uchicago (Doug Dougherty):
> (If I understand the original posting correctly, he is trying to read
> non-msdos disks)  Since absread() uses DOS, I doubt it could read
> non-DOS disks.  Or am I missing something???

Almost correct.

TC absread/abswrite use the DOS functions to read DOS' idea of what the
disk looks like. DOS reads (on a floppy) sector 0 to get the layout
of the disk; sector 0 is correctly set up (on a floppy) by the
DOS FORMAT command. You can use absread/abswrite on a non-DOS floppy,
as long as sector 0 contains the proper BIOS Parameter Block in bytes
11-28 of sector 0; this might well prevent reading diskettes written
by other operating systems. You can use absread/abswrite ONLY (i.e.
no open/fopen) on sectors 1-up to abswrite directly to the disk, and
absread it back again, without problems; you get no filenames, etc.

On a hard disk, sector 0 contains the partition table (I think), and
each partition contains its own BPB as on a floppy (values are 
different!).

Tom Roberts
att!ihlpl!tjrob  TJROB@IHLPL.ATT.COM