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