Date: Fri, 25 Oct 2002 10:11:44 +0100 (BST) From: Mark Valentine <mark@thuvia.demon.co.uk> To: "M. Warner Losh" <imp@bsdimp.com> Cc: cvs-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/lib/libdisk Makefile chunk.c write_alpha_dis Message-ID: <200210250911.g9P9BiCg064199@dotar.thuvia.org> In-Reply-To: <20021024.180030.103860565.imp@bsdimp.com>
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> From: "M. Warner Losh" <imp@bsdimp.com> > Date: Thu 24 Oct, 2002 > Subject: Re: cvs commit: src/lib/libdisk Makefile chunk.c write_alpha_dis > On the pc architecture you are requires to have a MBR. It is required to have a boot sector for the sake of the BIOS, containing boot code for the BIOS to hand off to; it is not required that this boot code implement a DOS-style partition table, and indeed a non-broken BIOS is completely unaware of any such partition table should it exist. The partition table was implemented by DOS code installed in the boot sector when you installed DOS. > All FreeBSD labeled disks > have a MBR on them, even the DD ones. With DD mode, the MBR is bogus > in that it doesn't describe the actual hardware. I repeat once more - any such implementation detail required to work around a broken BIOS need not (and should not) affect the user interface. > The problem here is one of historical usage. /dev/ad0a has worked on > FreeBSD since 0.0 and back into the 4.[34] BSD past before that. This labelling scheme continues to be sufficient (at least for up to 26 partitions without twisting it a bit). In fact it is all that exists for most BSD platforms and architectures. The complications introduced in an attempt to cater for multiple BSD disklabels on a disk are unnecessary and confusing, and in fact have been known to introduce problems (it seems that some PC partitioning tools don't care too much about retaining the order of entries in the partition table, making the hard-wired "slice" number problematic). System V made a similar mistake in embedding controller/unit numbers in the disk device name (at least FreeBSD allows wiring in the devices without affecting the device names, thank goodness). Cheers, Mark. -- Mark Valentine, Thuvia Labs <mark@thuvia.co.uk> <http://www.thuvia.co.uk>; "Tigers will do ANYTHING for a tuna fish sandwich." Mark Valentine uses "We're kind of stupid that way." *munch* *munch* and endorses FreeBSD -- <http://www.calvinandhobbes.com>; <http://www.freebsd.org>; To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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