Date: Thu, 17 Dec 2009 10:11:40 -0500 From: Jerry McAllister <jerrymc@msu.edu> To: Polytropon <freebsd@edvax.de> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: is this booting info correct? Message-ID: <20091217151140.GA40367@gizmo.acns.msu.edu> In-Reply-To: <20091217064959.e62bfdbb.freebsd@edvax.de> References: <4B296E66.6030405@a1poweruser.com> <20091217064959.e62bfdbb.freebsd@edvax.de>
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On Thu, Dec 17, 2009 at 06:49:59AM +0100, Polytropon wrote: > On Thu, 17 Dec 2009 07:33:58 +0800, Fbsd1 <fbsd1@a1poweruser.com> wrote: > > Users with Microsoft/Windows knowledge of how a hard drive is configured > > may have a terminology issue with FreeBSD. Microsoft/Windows and FreeBSD > > use the word partition to mean different (but related) things. > > > > FreeBSD and Microsoft/Windows have primary-partitions, but they call > > them different things. FreeBSD calls the Microsoft/Windows > > primary-partition a slice. > > FreeBSD's slice is a "DOS primary partition". > FreeBSD's partition is comparable (but not equal to) a "logical > volume inside a DOS extended partition". > > > The number of hard drive primary-partitions/slices is determined by the > > motherboard BIOS (Basic input output system), not the operating system. > > Standard motherboard BIOS limits hard-drives to 4 main divisions > > The limitation to 4 slices is due to DOS limitations that > are still present for legacy in the PC sector. But, the reason they are still present is that it is in BIOS. Of course, BIOS was written with old DOS in mind. Nowdays it has nothing to do with the OS. > > > Each of those are called primary-partitions in Microsoft/Windows > > terminology and slices in FreeBSD terminology. > > Yes. > > ... > > > They are > > implemented very differently and are not compatible with FreeBSD. > > I've not had problems accessing them so far. > >From FreeBSD, you can access almost anything because people in the FreeBSD community have written code to do it. > > > In > > FreeBSD the sub-divisions are called partitions. > > But only the subdivisions of a FreeBSD slice are called this > way. > Yup. And the OP is interested in FreeBSD. > > ... > > > The first physical track of the allocated space of each > > primary-partition/slice has an initial sector (512 byte block) that is > > called the boot sector. If it contains boot up code the motherboard BIOS > > considers it to be bootable. > > Yes. > No. It is the MBR that figures out if it is bootable. That is a step beyond BIOS. > > > Each physical hard drive in the PC has it's own MBR (Master Boot > > Record). The MBR is located in sector-0 of the first physical track on > > the hard drive. The standard MBR in Microsoft/Windows and FreeBSD > > defaults to booting the first primary-partition/slice allocated on the > > first hard drive cabled to the PC. > > No. The MBR usually branches to the first slice it finds that > has the bootable flag set. It doesn't have to be the first > one on the disk. Sort of. It has its own flag saying which one to boot and FreeBSD usually sets this as the last one booted. > > In case of FreeBSD, feel free to read "man boot" which gives > a good introduction to the topic. > > > > > There are MBR booting programs that you can load into the MBR on the > > first physical cabled hard drive to scan for other bootable > > primary-partitions/slices on this hard drive and any other hard drives > > cabled to the PC. It displays a menu giving you the option to choose > > which one you want to boot from. This gives you the ability to have more > > that one operating system installed on your PC at one time. > > Exact. > Not exactly. The BIOS goes down its list of boot devices which you can set and picks the first one it finds with an bootable MBR on it. loads that MBR and transfers control to it. Then the MBR controls the task of looking at its own slices for bootable ones loading one and transferring control to it. ////jerry > > -- > Polytropon > Magdeburg, Germany > Happy FreeBSD user since 4.0 > Andra moi ennepe, Mousa, ... > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org"
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