Edit an ArkOS / R36S SD card from your Mac

Updated August 2026 · ArkOS, Batocera, ROCKNIX, muOS

You flash ArkOS for your R36S, boot it, it works — then you plug the SD card into your Mac to add games and see either nothing at all or a scary "disk not readable" alert. Two separate things are going on, and both are fixable without borrowing a Windows PC.

Problem 1: the roms partition is hidden

ArkOS ships its FAT32 roms partition (EASYROMS) with the MBR partition type set to 0x1C — "hidden FAT32". Windows ignores the flag, which is why guides say "just use Windows". macOS respects it and refuses to mount the volume, even though it could read it perfectly. The fix is flipping one byte in the partition table so the type becomes plain FAT32 (0x0C). It's permanent, harmless, and the console doesn't care. Omnimount does it with the Unhide command; on Linux you'd use sfdisk.

Problem 2: the system partition is ext4

Configs, themes, saves and the OS itself live on an ext4 partition, which macOS can't read at all. To edit those files from a Mac you need an ext4 driver — see our full ext4 on Mac guide. With Omnimount, the partition shows up in the menu bar with a Mount button and appears like any other volume.

Adding ROMs and BIOS files

• Unhide EASYROMS once → it mounts automatically from then on, on any OS.
• Drag ROMs into the system folders (roms/gba, roms/snes…) in Finder.
• BIOS files usually go where the firmware expects them — check your firmware's wiki.
• Eject properly before pulling the card. FAT32 has no journal: a yanked card while copying is the #1 cause of corrupted libraries.

If the card stops booting

Run a filesystem check on the ext4 partition (e2fsck, or Omnimount's Check button) — a console frozen mid-save often leaves the journal dirty. And before any firmware update, clone the whole card to an image so you can restore it in minutes: see the cloning guide.