Date: Thu, 4 Jan 1996 11:39:25 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: bde@zeta.org.au (Bruce Evans) Cc: bde@zeta.org.au, terry@lambert.org, freebsd-hackers@FreeBSD.ORG, jkh@time.cdrom.com, obrien@cs.ucdavis.edu, phk@critter.tfs.com Subject: Re: X for install Message-ID: <199601041839.LAA18174@phaeton.artisoft.com> In-Reply-To: <199601040430.PAA11885@godzilla.zeta.org.au> from "Bruce Evans" at Jan 4, 96 03:30:54 pm
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> >Make sure the 32 bit absolute sector address in the partition table > >entry is correct. It won't be for DOS fdisk versions before 3.0x, > >and some utilities don't set it correctly. > > Such drives aren't supported. Checking the absolute sector address > requires knowing the BIOS geometry. Drivers already check it, based > on the guessed BIOS geometry, but since the BIOS geometry isn't known > for sure, inconsistencies aren't fatal, and since some users don't > like to see warnings at boot time, warnings about the inconsistencies > are disabled. So ask the BIOS by making a BIOS call from protected mode. It's the INT 13, AH=0x08, AL=<device> call. > >Fix the checksum after the AA55 (why isn't this done now?). > > There's no space after the AA55 :-). OK. Change that to "explain why the Compaq POST routines won't boot the machine because they checksum the entire boot area including the partition table and MBR". Then maybe add "Look at the LILO documentation that actually documents the checksum for Compaq and some other vendors". > >Then from protected mode *always* use the 32 bit sector offset > >instead of the C/H/S value. > > This has been done for a year. Even for locating the DOS partitions? I think it uses it's idea of the geometry from the partition table C/H/S values, but would be happy to be wrong. > >Much of this is documented in the PReP standard, which requires the > >use of the 32 bit offset/size value for PPCBug and for OpenBoot. > > The DOS3.x behaviour is the defacto standard. And is documented in the PReP standard, including extended partition handing. BSD can't use extended partitions (very well) yet. It should not require a disklabel entry to access DOS partitions. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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