Date: Fri, 5 Jan 1996 12:30:26 -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: <199601051930.MAA02568@phaeton.artisoft.com> In-Reply-To: <199601050756.SAA16788@godzilla.zeta.org.au> from "Bruce Evans" at Jan 5, 96 06:56:16 pm
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> >> 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. > > The BIOS doesn't work in protected mode :-). If you mean real mode, > it has been done for a year. See another discussion for why it isn't > sufficient. That's why I said "from" and not "in". the virtual 8086 will be running in "real mode" (assuming you had one). It's sufficient because you use MD5 checksums to differentiate the disks using protected mode and BIOS-based reads. If the disks are identical, you write a "safe area" (determined by FS type) to *force* them to be different. Everything is a lot easier with VM86(). 8-(. > >> >Fix the checksum after the AA55 (why isn't this done now?). > > >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". > > Compaq doesn't follow the industry standard of no error checking :-). LILO handles it correctly, however. Anyway, it's all *possible*, it's just a royal, royal pain. 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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