is this booting info correct?
jerrymc at msu.edu
Thu Dec 17 15:36:07 UTC 2009
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 at 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.
> > > 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.
> > --
> > Polytropon
> > Magdeburg, Germany
> > Happy FreeBSD user since 4.0
> > Andra moi ennepe, Mousa, ...
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