Date: Thu, 17 Dec 2009 10:32:01 -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: <20091217153201.GA40459@gizmo.acns.msu.edu> In-Reply-To: <20091217151140.GA40367@gizmo.acns.msu.edu> References: <4B296E66.6030405@a1poweruser.com> <20091217064959.e62bfdbb.freebsd@edvax.de> <20091217151140.GA40367@gizmo.acns.msu.edu>
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On Thu, Dec 17, 2009 at 10:11:40AM -0500, Jerry McAllister wrote: > 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. I may have overstated that. Even the most basic MBR (such as FreeBSD's) may be a little different from one OS to the next. The MBR chooses the slice, so it might be changeable from there. I haven't looked at that stuff in about 11 years. ////jerry > > > > 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" > _______________________________________________ > 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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