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From: cgs@umd5.umd.edu (Chris G. Sylvain)
Newsgroups: comp.os.minix
Subject: Re: Shoelace, Boot sector, Partition sector
Message-ID: <7502@umd5.umd.edu>
Date: 1 Nov 90 01:03:48 GMT
References: <34964@nigel.ee.udel.edu>
Reply-To: cgs@umd5.umd.edu (Chris G. Sylvain)
Organization: University of Maryland, College Park
Lines: 24

In article <34964@nigel.ee.udel.edu> TEMARI%ECAMV1.dnet.ge.com@vm1.nodak.edu writes:
>The first byte of each partition entry contains the so called flag for active
>partition, which happens to be 80h (i.e. hard disk 0).  According to Gordon W.
>Ross (gwr@linus.mitre.org) the code he gave loads dl (i.e. the drive to read
>the boot sector from) from the first byte of the partition table entry.

The partition status byte is the first byte in the partition table. A value
of 0x80 indicates the referenced partition described in the following 15 bytes
is an active and bootable partition. That is all the 0x80 value signifies. It
has nothing to do with the drive number other than the coincidence that when
the first fixed disk drive is referenced by number, the value 0x80 is used.

Parition tables are used within the context of the currently accessed fixed
disk drive. There is no value in the partition table indicating for which disk
the table is valid. Since one disk must be selected to be able to read the
partition tables, then the disk for which the table is valid is already known.

Therefore, if the Gordon Ross' code does what is described above, then DL will
always have the value 0x80 or 0x00, and never 0x81 nor 0x01.
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