UEFI support in ArcaOS 5.1 – update for February, 2022

Development and testing of Arca Noae’s support for UEFI continues. Here’s a brief recap of how this will work in ArcaOS 5.1:

When the installation media boots, if the system is determined to be in “UEFI mode” as opposed to “Legacy mode” (“Legacy” here refers to the configuration which presents a traditional PC BIOS), ArcaOS will begin the preboot process using its compatibility system. Essentially, this is a 64-bit environment which will provide a rather complete BIOS emulation for the ArcaOS kernel, including VGA services for video display.

If the user selects to use his own settings for installation (the preboot menu), the screens will look and act just like a traditional installer boot, but will, in fact, be provided by this new compatibility system.

Once control is handed off to the ArcaOS kernel, the OS itself is exactly the same as a traditional ArcaOS boot. That is to say, the kernel is identical. The goal of the Arca Noae Compatibility System (ANCS) is to provide a standard environment for ArcaOS, without the need to actually maintain different versions of ArcaOS files for each environment. Another benefit of ANCS is that because the video BIOS emulation is generally more complete than that provided by the CSM in many systems built in the past decade, DOS and Win-OS/2 sessions tend to run much better.

ArcaOS 5.1 should support booting in UEFI mode on a range of systems which provide a recent UEFI implementation, from either GPT or MBR partitioned disks. In the next post in this series, we’ll discuss GPT and MBR and how the boot process differs between the two partition layouts.