ArcaOS, an updated version of IBM OS/2, is adding experimental support for booting via UEFI as Intel is phasing out the legacy BIOS interface in 2020.
OS/2—which was, at one time, IBM’s competitor to Windows—continues to enjoy an extended afterlife, following the end of principal development in 1996. In 2015, Arca Noae announced a new, licensed distribution of OS/2—bundling new software and device drivers written for OS/2 with a new installer—with initial release in 2017 as ArcaOS 5.0 “Blue Lion.”
Maintaining a decades-old operating system presents a variety of development problems far outside the mainstream, with solutions for those problems requiring a great deal of creativity to not break compatibility with existing drivers or programs. One of the most pressing issues facing OS/2 is the impending removal of the legacy BIOS Compatibility Support Module (CSM) starting in January 2020.
Compared to DOS, which extensively utilizes BIOS functionality, OS/2 has hard dependencies on only a subset of BIOS features, according to Arca Noae developer Alex Taylor, in a presentation at Warpstock Europe, posted to YouTube this week. The BIOS-supplied INT10 and INT13—VGA hardware and disk I/O via BIOS, respectively—are needed to boot ArcaOS.
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As a quick overview, in Windows or Linux, the necessary files or drivers are loaded via BIOS or UEFI, after which the kernel is executed. For UEFI, most—if not all—the UEFI code is unloaded after it completes its task, while BIOS code largely remains in memory. The boot sequence in OS/2 complicates a move to UEFI, as a subset of services are loaded through the BIOS, after which the OS/2 native disk controller takes over, loading the remainder of the data needed to start the Workplace Shell.
The Arca Noae-provided UEFI loader does support major system components, and while ArcaOS does boot at present, the technical proof-of-concept presented at Warpstock Europe does not yet support VDM—the compatibility layer for DOS and Windows 3.11 support—nor does it yet support loading system files from the partition, or memory dump support. Special handling of filesystem data—moving from MBR to GPT is also an important consideration—will require additional development.
Likewise—while ArcaOS can boot and install from USB—additional drivers for USB 3 are needed to boot on USB on devices utilizing UEFI but not shipping with CSM support.
Support for booting via UEFI has not yet been released, though the modern OS/2 distribution ArcaOS is available as a download from Arca Noae. Personal licenses are $129, with commercial licenses at $229. Personal licenses include six months of updates and technical support, commercial licenses include one year of updates and priority technical support.