Linux › Section E · How the Linux kernel boots › Topic E.5
Boot loader details: MBR and UEFI boot
PCs start boot loaders in two very different ways. Legacy BIOS boot squeezes code into the first sector of a disk; UEFI boot reads ordinary files from a small FAT partition and keeps a list of boot entries in firmware memory. Knowing both explains where GRUB really lives and how to repair it.
In this topic
- Two ways to start a PC
- Inside the 512-byte MBR
- Worked example: the MBR and the gap
- Multistage MBR boot
- GPT disks with a BIOS
- UEFI boot and the EFI system partition
- Boot entries in NVRAM
- Worked example: reading efibootmgr
- How GRUB gets going, in both modes
- Common mistakes to avoid
- Key takeaways
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