Bring BIOS support

content/news/20251006-bringing-bios-support.md

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+title = 'ExectOS Expands Beyond UEFI: Bringing BIOS Support'
+author = 'Aiken Harris'
+date = '2025-10-06T10:36:18+01:00'
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+When we first started building ExectOS, we envisioned it as an operating system designed exclusively for UEFI-based
+systems. Over time, however, we realized that this requirement was an artificial limitation. Today, we are excited to
+announce that we have begun taking concrete steps toward supporting traditional PC/AT hardware with classic
+BIOS - broadening the reach of ExectOS to a much wider range of systems.
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+
+## First Steps Toward BIOS Compatibility
+We have already implemented an MBR boot sector and updated our CMake configuration to support BIOS-based emulation. As
+of now, ExectOS can be launched in several new testing configurations:
+ * **bochsvm**: Bochs with BIOS
+ * **testkvm/testtcg**: QEMU with classic BIOS (with KVM/WHPX acceleration or TCG without acceleration)
+ * **testefikvm/testefitcg**: QEMU with modern UEFI (with or without acceleration), as before
+
+This means developers can now experiment with ExectOS under both UEFI and BIOS environments using familiar tools like
+Bochs and QEMU.
+
+## A Unified Boot Partition Model
+To simplify BIOS support, we are introducing a dedicated BOOT partition - similar to the recommended practice on
+Unix-like systems and analogous to the ESP (EFI System Partition) used by UEFI. Our bootloader will exclusively support
+FAT32 on this partition. It will house the bootloader itself, its configuration, and all modules. In other words, we are
+effectively bringing the concept of the ESP from the UEFI world into the BIOS realm.
+
+## What's Next?
+Full BIOS support is still some way off. The current MBR implementation and CMake adjustments are just the first step. We
+still need to:
+* Implement a VBR (Volume Boot Record) capable of locating and loading files from disk
+* Develop a preloader to prepare the environment for the main bootloader (enabling paging, long mode, etc.)
+* Significantly refactor XTLDR, to eliminate assumptions about UEFI, such as memory allocation APIs
+* Ensure all modules are environment-agnostic, running seamlessly on both BIOS and UEFI systems
+* Move PE/COFF file handling from the module level into the main XTLDR code
+
+While there is still a long road ahead, this change opens up new possibilities for ExectOS. By removing the UEFI-only
+limitation, we are making the system more flexible and accessible.