BIOSlegacy

BIOSLegacy is a software project and standard aimed at preserving compatibility with legacy BIOS interfaces within modern firmware ecosystems. It provides a portable, open-source layer that emulates traditional BIOS services so operating systems and bootloaders written for BIOS can operate on systems that use UEFI or other modern firmware. By offering a BIOS API layer, an emulated BIOS core, and device drivers for common legacy hardware, BIOSLegacy seeks to reduce migration friction when moving from BIOS-based systems to newer platforms.

BIOSLegacy interacts with the host firmware through a modular stack that includes a BIOS API façade, an interrupt translation layer (for software relying on BIOS interrupts), and a boot manager that can chainload legacy boot sectors or bootloaders. The project supports both in-VM emulation and hardware environments where a traditional Compatibility Support Module would otherwise be unavailable or undesirable.

Key features include support for legacy video BIOS calls (int 10h), disk BIOS routines (int 13h), and basic real-mode memory addressing; MBR-to-GPT compatibility helpers; and a pluggable set of drivers for common legacy devices such as VGA, floppy, and AT keyboard interfaces.

Origin and development: The project emerged from community discussions in the early 2020s as a response to growing fragmentation between legacy systems and UEFI-only environments. It is maintained by an international developer community and is released under a permissive open-source license.

Impact and reception: It has been adopted in virtualization platforms and some hardware compatibility demos; some critics warn of added security and performance overhead and potential duplication of firmware responsibilities.