BIOS boot partition

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A BIOS boot partition is a partition on a data medium that uses the Grand Unified Bootloader (GRUB) on a BIOS -based PC to boot an operating system if the current boot medium has a GUID partition table (GPT).

Basics

A BIOS boot partition is required on GPT-partitioned data carriers in order to store the data of the second level of the GRUB. On MBR-partitioned data carriers, the data blocks immediately following the first data block are normally not used because the partitioning scheme cannot determine them for a specific purpose and the partitioning tools avoid them for alignment purposes. On GPT-partitioned data carriers, these data blocks contain the actual partition table, so an additional partition is necessary. On MBR partitioned disks, boot loaders are usually implemented in such a way that the part of their code that is stored in the MBR and cannot contain more than 512 bytes acts as the first stage, which is mainly used to load a more complex second stage. This second level is able, for example, to read and load an operating system kernel from a file system .

Overview

In Example 2, GRUB 2 saves its core.img in a BIOS boot partition.

When used, the BIOS boot partition contains the second level of the boot loader program, e.g. B. GRUB 2 . The first stage is the code contained in the Master Boot Record (MBR). Using this partition is not the only way to perform a BIOS-based boot with GPT-partitioned disks. Complex boot loaders such as GRUB 2 do not fully fit within the limits of the MBR (398 bytes (MBR with hard disk time stamp, hard disk signature, AAP and NEWLDR support) to 446 bytes (classic MBR without extensions)). Therefore, they need additional storage space. On MBR-partitioned data carriers, such boot loaders normally use the data blocks that immediately follow the MBR for this purpose. This area is often referred to as the “MBR gap” (German: “MBR gap”). There is no equivalent unused space on GPT-partitioned volumes; and the BIOS boot partition is a way to officially assign this space to the boot loader.

The Universally Unique Identifier (UUID) for a BIOS boot partition in GPT is 21686148-6449-6E6F-744E-656 564 454 649 , resulting in the GPT in the necessary little endian scheme , the ASCII - string " ! Hah IdontNeedEFI " results.

A BIOS boot partition requires relatively little space. When partitioning, you usually set up 31 KB of space for them.

Manufacturing

The following programs can be used to create BIOS boot partitions. However, it depends on the versions.

Web links

Individual evidence

  1. ↑ GNU GRUB Manual 2.04: BIOS installation
  2. ↑ Magic Numbers: The Secret Codes Programmers Hide on Your PC - www.phhsnews.com