Translation wiki (i): Bios boot partition

Article translation from the wiki, the level is limited, if the wrong million please forgive me. Original:https://en.wikipedia.org/wiki/BIOS_boot_partition

The BIOS boot partition is a partition, and GNU Grub[1] uses it to boot an operating system that is based on the legacy BIOS but contains a GPT-formatted partitioned table on the boot device. This structure is sometimes referred to as bios/gpt startup [2].

Non-original content, is provided by me, used to intuitively feel the BIOS boot partition.

The Bios boot partition is necessary because GPT uses the sector immediately following the MBR to hold the actual partition table, but in the traditional MBR partition architecture, these sectors do not have a special effect, so the result is that there is not enough free space available to store the Stage2 boot loader. The boot loader is also stored in the MBR, but the MBR cannot store more than 512 bytes of content, so the boot loader in the MBR is used as a stage1, and its main function is to load more and more complex stage2 this boot loader, Stage2 can read from and load the operating system kernel from the file system.

When a BIOS boot partition is used, the partition will contain the boot loader program for stage2, such as the Grub2 file, and stage1 boot loader code remains in the MBR. Using the BIOS boot partition is not the only way to resolve a problem based on the traditional BIOS but using the GPT format disk, but complex boot loader such as GRUB2 cannot fully conform to the 398-446-byte zone in the MBR, so they require a secondary storage space. On MBR disks, it is common to use the sector space immediately following the MBR to store these complex boot loader, which are known as the "MBR gap" in the public area. On GPT disks, because there is no unused space equivalent to the MBR gap, a single BIOS boot partition is used to allocate this space to store the complex boot loader.

The GUID of the BIOS boot partition can be "21686148-6449-6e6f-744e-656564454649". In GPT under the BIOS-based platform, the BIOS boot partition is somewhat similar to the EFI system partition under the EFI platform, the EFI system partition uses UEFI to save the file system and files, and the BIOS boot partition for the BIOS platform does not use the file system to save the code (see figure above, The file system was not created on the BIOS boot partition).

The BIOS boot partition size is very small and can be as small as 31kB (since the first sector is MBR, the BIOS boot content is from the 2nd sector to the 63rd sector), but since the future boot loader may expand, it is recommended that the BIOS boot partition be set to 1M size, And many disk partitioning tools use 1MB partition alignment policies, so that some free space is retained between the MBR and the first partition.

In Example 2, Grub 2 stores its core.img in the BIOS boot partition.

[1]gnu Grub: The grub that is now used is the GNU cottage, and the original grub has long been lost in history.

[2]: This is the BIOS MBR and GPT mixed mode.

Reprint Please specify source:http://www.cnblogs.com/f-ck-need-u/p/7084627.html

Translation wiki (i): Bios boot partition