OS/2, eCS & ArcaOS - Technical > Setup & Installation

Booting eCS and MCP under UEFI


Rich Walsh:

If you installed ArcaOS 5.1 in UEFI mode on a machine that also supports CSM/BIOS, the instructions below will allow you to boot your existing eCS or MCP installations alongside your new 5.1 system - all while remaining in UEFI mode. This procedure requires no changes to your legacy installations, and only two small changes to AOS 5.1's 'config.sys'. The primary downsides here are that you will lose 5.1's DOS video enhancements, and the  AOS boot logo will no longer be displayed.

Note: this procedure can also be used to restore 16x9 resolutions on older machines that only offer 4x3 video when booted in UEFI mode.


TTBOMK, the following instructions are complete and correct, and should be followed exactly as written.

1. Confirm the machine is in UEFI mode and that CSM is enabled.

2. Assign a drive letter to your EFI partition (e.g. 'U:') then open the folder 'U:\EFI\OS2'.
    Create a new file in this directory named 'OS2LDR.CFG' that contains this single line:

--- Code: ---alt_video = 1

--- End code ---

3. On your AOS 5.1 install, open 'config.sys' in an editor. Change these two entries as shown:



--- End code ---


--- Code: ---rem DEVICE=C:\OS2\MDOS\VEFI.SYS


--- End code ---

4. In your boot manager's config file, add entries for your BIOS-based installs that are identical
    to the one you have for AOS 5.1, with the only difference being the drive letter to be booted.

    For example, if eCS 2.x is on your E: drive, its entry in 'launcher.cfg' would look like this:

--- Code: ---eCS 2.x (E:) = \EFI\OS2\OS2LDR.EFI E:

--- End code ---

    In 'refind.conf', it would look something like this:

--- Code: ---menuentry "eCS 2.x (E:)" {
    loader \EFI\OS2\OS2LDR.EFI
    options "E:"

--- End code ---

5. Reboot.


* This is a machine-wide change that affects all AOS 5.1 UEFI installs. If you have more than one, update 'config.sys' for each.
* Do not make any changes to your BIOS-based installs in connection with this - it should all "just work" with no user intervention.
* This has only been tested with Panorama. Regardless, SNAP should work as well.


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