BIOSLegacyBoot
BIOSLegacyBoot describes the boot pathway that lets a system with modern firmware boot operating systems and bootloaders designed for legacy BIOS. On UEFI systems, this is provided by the Compatibility Support Module (CSM), which emulates a BIOS environment. Legacy boot can also use an MBR disk in BIOS compatibility mode.
Background: As UEFI supplanted BIOS, firmware makers retained legacy support to run older software that relies
How it works: On power‑on, firmware may select a legacy path. If enabled, the CSM emulates BIOS
Compatibility and limitations: BIOSLegacyBoot enables booting of systems installed in legacy mode but disables Secure Boot
Usage and migration: For new systems, UEFI with GPT is recommended for security and features. If legacy
See also: BIOS, UEFI, Compatibility Support Module, MBR, GPT, Secure Boot, bootloader.