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When Secure Boot is enabled, it is initially placed in "setup" mode, which allows a public key known as the "platform key" (PK) to be written to the firmware. Once the key is written, Secure Boot enters "User" mode, where only UEFI drivers and OS boot loaders signed with the platform key can be loaded by the firmware.
Prior to the development and ubiquitous adoption of the Plug and Play BIOS standard, an add-on device such as a hard disk controller or a network adapter card (NIC) was generally required to include an option ROM in order to be bootable, as the motherboard BIOS did not include any support for the device and so could not incorporate it into the BIOS's boot protocol.
When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk, a floppy disk, CD, or DVD. It loads and executes the first boot software it finds, giving it control of the PC. [28] The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches.
A Trusted Platform Module (TPM) is a secure cryptoprocessor that implements the ISO/IEC 11889 standard. Common uses are verifying that the boot process starts from a trusted combination of hardware and software and storing disk encryption keys. A TPM 2.0 implementation is part of the Windows 11 system requirements. [1]
You can disable Secure Boot by restarting your PC and opening the Unified Extensible Firmware Interface (UEFI).
If UEFI Secure Boot is supported, a "shim" or "Preloader" is often booted by the UEFI before the bootloader or EFI-stub-bearing kernel. [11] Even if UEFI Secure Boot is disabled this may be present and booted in case it is later enabled. It merely acts to add an extra signing key database providing keys for signature verification of subsequent ...
According to an AMD developer's guide, the subsystem is "responsible for creating, monitoring and maintaining the security environment" and "its functions include managing the boot process, initializing various security related mechanisms, and monitoring the system for any suspicious activity or events and implementing an appropriate response". [2]
When GRUB is installed on a hard disk, boot.img is written into the boot sector of that hard disk. boot.img has a size of only 446 bytes. A boot sector is the sector of a persistent data storage device (e.g., hard disk , floppy disk , optical disc , etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed ...