Path: utzoo!utgpu!watmath!clyde!feg
From: feg@clyde.ATT.COM (Forrest Gehrke)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Boot sector of harddisk?
Keywords: where is it?
Message-ID: <38656@clyde.ATT.COM>
Date: 27 Dec 88 14:50:39 GMT
References: <6941@xanth.cs.odu.edu>
Distribution: na
Organization: AT&T Bell Labs, Whippany NJ
Lines: 31

In article <6941@xanth.cs.odu.edu>, kahn@xanth.cs.odu.edu (Gary I Kahn) writes:
> The boot sector on a floppy disk is at head 0, track 0, sector 1.
> Can someone tell me where the corresponding sector is on a hard disk?
> I'm trying to locate the bytes on the disk which give information about
> the number of sectors, heads, and tracks.  I tried using INT 13 to read
> the sector mentioned above (0/0/1), but it turned out to not be the
> boot sector.  The disk-editor utilities I tried use logical sector numbers,
> not tracks and heads.  Thanks in advance.

Unlike floppy disks, the HD uses the first sector as the partition
sector, and this is the sector you accessed. The last 4 paragraphs
of the 512 bytes of this sector list the data of the 4 possible
partitions of the HD.  The bootable partition paragraph begins
with hex 80 and this paragraph will have the head, cyl and
sector info for the boot sector.  If memory serves me, using
INT 13, the boot sector is located as 0/1/0.  You can identify
the boot sector by looking at bytes (decimal) 4 through 11.
This will give information including the msdos version number.
Somewhere around the end of this sector you will see listed
the two hidden file names.
If you are not sure what the boot sector looks like, try this:
In debug:    l ds:1000 2 0 1
             d ds:1000 l200

The first command loads the first relative sector of the C disk
to memory starting at ds:1000
The second command reads the 512 (decimal) bytes of the boot
sector.  Debug can not access the partition sector.

Forrest Gehrke