Date: Tue, 29 Dec 2009 09:24:40 +0800 From: Fbsd1 <fbsd1@a1poweruser.com> To: Polytropon <freebsd@edvax.de> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: re-write is this booting info correct? Message-ID: <4B395A58.7010801@a1poweruser.com> In-Reply-To: <20091228151416.07a2f22d.freebsd@edvax.de> References: <4B296E66.6030405@a1poweruser.com> <20091217064959.e62bfdbb.freebsd@edvax.de> <20091217151140.GA40367@gizmo.acns.msu.edu> <4B38ACF9.2050705@a1poweruser.com> <20091228151416.07a2f22d.freebsd@edvax.de>
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Polytropon wrote:
> On Mon, 28 Dec 2009 21:04:57 +0800, Fbsd1 <fbsd1@a1poweruser.com> wrote:
>> The Microsoft/Windows fdisk program is used to allocate partitions on
>> the hard drive. This program allocated two types of partitions “primary
>> dos partition” and “extended dos partition”.
>
> Just a formal addition: "primary DOS partition" - DOS stands
> for "Disk Operating System", it's an abbreviation. You're
> stating this later on, but you should do it at its first
> occurance.
>
>
for correctness i agree.
>
>> A single “primary dos partition” occupying all the space on the hard
>> drive would be assigned drive letter C.
>
> The "drive letters" used seem to include the ":" as a part,
> so it would be "C:" instead of plain "C".
>
>
I have the win98 fdisk english version. I tested this and the fdisk
program displays just the drive letter with out the :. Now on the DOS
command line you do have to use the : to change to different drive, like
in to change to A: drive.
>
>> An alternate method is to allocate an “extended dos partition” and then
>> sub-divide it into logical dos drives lettered C, D, E, F.
>
> I think the term is "logical volume inside an extended DOS
> partition"; I'm not very familiar with their english names,
> but that would correspond to the correct german name (found
> in german versions of DOS); the term is "volume" or "drive".
>
> I've got no english DOS documentation here, so I can't
> check for the correct term.
>
> German: "Primäre DOS-Partition" and "Logisches Laufwerk in
> einer erweiterten DOS-Partition", and "Laufwerk" means
> "drive", but I think I recall that DOS uses "volume" for
> this...
>
The correct word as displayed in the fdisk program is 'logical dos
drives' just the way i have it.
>
>
>> One of these
>> “primary dos partitions” or one of the logical dos drives in the
>> “extended dos partition” must be set as the active partition to boot
>> from.
>
> I'm not sure you can actually boot from a logical volume
> inside an extended DOS partition... as far as I remember,
> booting can only take place from a primary DOS partition.
>
>
I tested this and can confirm you can boot from a logical drive
inside an extended DOS partition. Just have to set the active flag first.
>
>
>> FreeBSD’s fdisk program allocates disk space into slices. A FreeBSD
>> slice is the same thing as a Microsoft/Windows “primary dos partition”.
>> FreeBSD has nothing akin to an “extended dos partition”.
>
> It quite has - its slices (which are subdivided just as the
> extended DOS partitions are, so its partitions are like -
> but not the same as - the logical volumes inside a DOS
> extended partition).
>
>
>
>> The
>> Microsoft/Windows partition and the FreeBSD slice is where the operating
>> system software is installed.
>
> No. The software is installed on the partitions inside a
> slice, or, to be more exact, in the file system that the
> partition holds. There can be of course one partition
> coviering the whole slice, so "partition(s)" would be
> a valid term.
>
>
>
>> The FreeBSD
>> ‘disk label’ program is used to sub-divide the slice into smaller chunks
>> called partitions. In a standard install of FreeBSD, these partitions
>> are the default directory names used by the operating system.
>
> Not "are" - they _refer_ to them (or are refered to by
> then), e. g. the default directory name / is the root
> directory, but /dev/ad0s1a is the partition; /usr is the
> directory for { UNIX system resources | user binaries and
> libraries }, but /dev/ad0s1g is (maybe) the partition that
> holds this data. In settings where one partition convers
> the whole slice, there are no further mountpoints for the
> divisions of functional parts of the system.
>
>
>
>> The motherboard standard which was created in the days before windows
>> desktop were even though of yet and at which time Microsoft DOS (disk
>> operating system) was the only thing available.
>
> Sure. :-)
>
>
>
>> This hard drive 512-byte MBR is where all the limitations are. Do to
>> it’s size the MBR partition table is limited to 4 entries.
>
> Due to its size...
good catch.
>
>
>
>> This means no
>> matter how large your hard drive is (20MG or 200GB) you can only
>> sub-divide it into a maximum 4 slices/partitions.
>
> 20MB. But I'd like to have a 20 machine gun hard disk, too. :-)
>
back in win3.1 days a 20MG hard drive was the largest made at the time.
>
>
>> The default MBR code written by the Microsoft/Windows fdisk program is
>> hard coded to boot the C drive. The FreeBSD fdisk program has option to
>> write a simple boot menu program to the MBR.
>
> You could add that this program is called the "FreeBSD boot
> manager", because that's its actual name.
>
>
>
> Everything else seems to be correct to me, as well as
> written in an appealing way, and technically understandable.
>
>
I am adding this verbiage to my FreeBSD installer Guide for
release 8.0 which will be available to the public 1/1/2010 at
http://www.a1poweruser.com/
following is the corrected version incorporating your ideas.
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.
The Microsoft/Windows fdisk program is used to allocate partitions on
the hard drive. This program allocated two types of partitions “primary
dos partition” and “extended dos partition”. DOS means “disk operating
system” which was the precursor to the Microsoft/Windows desktop GUI
“graphical user interface” first appearing in Win 3.1.
A single “primary dos partition” occupying all the space on the hard
drive would be assigned drive letter C. You can also sub-divide the hard
drive into multiple “primary dos partition” each one being assigned a
drive letter C, D, E, F. An alternate method is to allocate an “extended
dos partition” and then sub-divide it into logical dos drives lettered
C, D, E, F. One of these “primary dos partitions” or one of the logical
dos drives in the “extended dos partition” must be set as the active
partition to boot from. In a multiple partition allocation only one
partition can be marked as bootable at one time. Typically legacy
Microsoft/Windows Win3.1, Win95, Win98, WinMe, and Win2000 defaulted to
a single “primary dos partition”. Starting with XP, PC manufactures
started to provide support for their PC’s operating system by having a
second “primary dos partition” where the original factory version of
the system was hidden and used to restore the C drive back to the
factory version when corrupted by a virus. Microsoft/Windows provides no
native method of selecting which partition to boot from in a multiple
partition allocation.
FreeBSD’s fdisk program allocates disk space into slices. A FreeBSD
slice is the same thing as a Microsoft/Windows “primary dos partition”.
The FreeBSD ‘disk label’ program is used to sub-divide the slice into
smaller chunks called partitions. FreeBSD partitions are like (but not
the same as) the logical drives inside a “extended dos partition”.
The motherboard standard which was created in the days before windows
desktop were even though of yet and at which time Microsoft DOS (disk
operating system) was the only thing available. This legacy standard has
continued un-updated to this current time and contributes to the
limitations imposed on booting, disk layout and selection of which
allocation on the hard disk to boot from.
The motherboard BIOS ROM chip at power up inquires each device
(floppies, cdrom, hard drive, usb memory stick) you selected in the BIOS
menu to boot from.
The hard drive has a MBR (Master Boot Record) a (512 byte block) located
in sector-0 of the first physical track on the hard drive. This MBR
contains bootstrap code and the disk partition table created by the
fdisk program. The BIOS boot code reads the MBR code and disk partition
table into memory and then transfers control to it. This MBR code is
responsible for parsing the partition table and finding the bootable
slice/partition that is marked 'active'. The MBR code then sets up the
disk-address-offset information for the bootable slice/partition, and
reads 'relative sector zero' from that slice/partition, and transfers
control to that one-sector block of code that contains the unique
operating system code to load it into memory.
This hard drive 512-byte MBR is where all the limitations are. Due to
its size the MBR partition table is limited to 4 entries. This means no
matter how large your hard drive is (20MG or 200GB) you can only
sub-divide it into a maximum 4 slices/partitions.
The default MBR code written by the Microsoft/Windows fdisk program is
hard coded to boot the C drive. The FreeBSD fdisk program has option to
write a simple boot menu program to the MBR. Its called the "FreeBSD
boot manager".
There are MBR boot menu programs in the FreeBSD ports collection 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.
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