Date: Thu, 15 Jun 1995 13:09:11 +1000 From: Bruce Evans <bde@zeta.org.au> To: hlew@genome.Stanford.EDU, terry@cs.weber.edu Cc: bugs@FreeBSD.org Subject: Re: 2.05R panics on boot Message-ID: <199506150309.NAA27850@godzilla.zeta.org.au>
next in thread | raw e-mail | index | archive | help
>The DOS MBR: >,------.---------------------.-------------------. >| JUMP | DOS PARTITION TABLE | DOS MBR BOOT CODE | >`------'---------------------'-------------------' >The DM MBR: >.------.-------------------------.---------------. >| JUMP | FAKE DOS PARTIOTN TABLE | DM MAGIC CODE | >`------'-------------------------'---------------' There is code between the JUMP and the PARTITION TABLE too. >The PBR (partition boot record; second stage boot): >> Do I subtract 64 from the sector number while in the FreeBSD install >> program under disk partitioning or are you referring to a DOS utility to >> do this? A driver should subtract it. >OK, DM has a boot record it writes on the drives that's 63 or so sectors >long (depends on the version, etc.). FreeBSD assumes the fixed value 63 (for DM partition type 84). >Now what is "OS-BS", "BootEasy", "LILO", the"OS/2 Boot Manager", etc. going >to do? >... >OK, now say you boot off a BSD floppy. >You are still screwed, because even if it had loaded the DM MBR and patched >INT 13, except for actually loading, the BSD code doesn't use the BIOS >at all. Not that you could load the DM MBR anyway, if you boot off a >floppy. >Now BSD's new slice code knows about the DM MBR. But the installation >of the MBR code does not. Yes it does (modulo bugs). Only one case can't possibly work: loading the bootstrap off a floppy and then attempting to boot from a hard disk (e.g., by typing sd(1,a)/kernel). The boot code doesn't know about DM, so it won't work if DM needs to be loaded. Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199506150309.NAA27850>