www.aei.mpg.de/~pau/zen_process_obsd.html
2008/7/18 Josh Grosse <[EMAIL PROTECTED]>:
> On Fri, Jul 18, 2008 at 04:23:38AM -0400, x x wrote:
>> anyone successfully dual boot with Linux, as well separately dual booting
>> with XP/Vista?
>
> Sure.
>
>> I read through the FAQ about Linux and that is 4 years old, and am having
>> a major pain and frustration with CHS, same with XP machine, having problems
>> around the setting the CHS.
>
> You should not have to set CHS values with a modern (say, less than 15 years
> old) BIOS. The drive tells the BIOS what it prefers, and the BIOS should
> use that.
>
>> Also in fdisk, in faq for mutibooting only shows 0 is Win-95, 1, 2, and 3
>> or unused so e 1, but what if 0, 1, and 2 are each used from a Linux
>> distribution, do I e 3, but which do I set as the active partition, do I
>> f 0 or f 1 and write to disk for Linux, or do I f 3 and write to disk to
>> boot Open?
>
> You need to understand this much about Master Boot Records, and MBR
> partitions:
>
> It's a very old design. There is only room in the MBR for 4 partitions.
> These are called, "Primary Partitions". An "Extended DOS Partition" is a
> method of increasing that number without changing the structure of this old
> design; one of the 4 partition slots are used to point to blocks on disk
> with additional MBR partitions. This design was invented by Microsoft to
> add some logical partitions without impacting any of their PC manufacturing
> cusotmers.
>
> Some OS's are very particular about starting and ending addressing and
> booting.
> It is usually best to use each OS's MBR manipulation tools when setting up
> multibooting. Windows tools for Windows, Linux tools for Linux, and OpenBSD
> tools for OpenBSD.
>
> Today, OpenBSD requires a primary partition. Using OpenBSD's fdisk(8)
> program, these are numbered 0-3. If, as you say, on your system 0-2 are used
> and 3 is unused, then you must use 3. If all four are already in use, you
> must restructure your system to free one of these primary partitions.
>
> The "f" command you mention, "flag", is used to assign the active, bootable
> partition for the BIOS.
>
>> When I set CHS to work along side XP on there and reboot nothing works,
>> neither OS knows how to load
>
> On boot, the BIOS loads the MBR program from the drive. The partition marked
> as bootable ("active" in Microsoft's fdisk program, "flagged" in OpenBSD's)
> is determined, and its Partition Boot Record (PBR) is loaded and executed.
> If none of the four partitions is marked active, the disk is not bootable.
>
> Below, is the output of "# fdisk wd0" on a laptop with three operating
> systems:
> WXP, Ubuntu, and OpenBSD. There are 4 primary partitions in use, one for
> each OS and a fourth, containing the "Extended DOS Partition" which is used
> by Ubuntu to create a logical partition for Linux swap.
>
> Note the "active" partition is OpenBSD; though I use the GAG bootloader to
> manage multibooting -- it lives in the blocks before partition #0 begins.
>
> Disk: wd0 geometry: 2432/255/63 [39070080 Sectors]
> Offset: 0 Signature: 0xAA55
> Starting Ending LBA Info:
> #: id C H S - C H S [ start: size ]
> -------------------------------------------------------------------------------
> 0: 07 0 1 1 - 522 254 63 [ 63: 8401932 ]
> HPFS/QNX/AUX
> *1: A6 523 0 1 - 1815 254 63 [ 8401995: 20772045 ] OpenBSD
> 2: 83 1816 0 1 - 2401 254 63 [ 29174040: 9414090 ] Linux
> files*
> 3: 05 2402 0 1 - 2431 254 63 [ 38588130: 481950 ] Extended
> DOS
> Offset: 38588130 Signature: 0xAA55
> Starting Ending LBA Info:
> #: id C H S - C H S [ start: size ]
> -------------------------------------------------------------------------------
> 0: 82 2402 1 1 - 2431 254 63 [ 38588193: 481887 ] Linux swap
> 1: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused
> 2: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused
> 3: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused
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