R36S microSD Master Image Cloning (macOS + Terminal dd)
Congrats on getting an r36s system. You've entered a rabbit hole of history, preservationism, fun times, and the philosophy of intellectual property. The cheap retro device you hold in your hands is basically a museum, but it's falling apart. Luckily, there's one main component that can be easily replaced to keep this device running for years: the SD card.
This write-up documents the exact process we can use to make a master image of a working r36s microSD card and then clone it onto one or more new microSD cards using macOS Terminal.
As you can see in this writeup, the steps are highly specific and during this process you have the power to destroy your computer. So, I recommend asking chatGPT or another AI of your choice to walk you through this process step by step. Tell your AI about your exact situation and copy-paste to it your terminal output if you can't give it direct access. You can even ask your AI to reference this article.
Big Safety Rule
dd can destroy data instantly if you point it at the wrong disk.
Always confirm the target disk number with diskutil list before running dd.
Your internal Mac drive is almost always /dev/disk0 — do not touch it.
Table of Contents
1) Requirements 2) Why this works (and why Disk Utility images may fail) 3) Create the master raw image from the ORIGINAL SD 4) Clone the master image to a NEW SD 5) Repeat for additional SD cards 6) Verify + expected macOS popups 7) Notes: partitions, saves, and extra space1) Requirements
- A working R36S microSD card (the “original” that boots your device)
- One or more new microSD cards (equal or larger capacity is ideal)
- A microSD reader connected to your Mac
- An external drive (HDD/SSD) with enough free space to store the image (≈ the size of the original SD)
2) Why this works (and why Disk Utility images may fail)
R36S/ArkOS boot media relies on partition tables and boot sectors that are not preserved by simple file copying.
Disk Utility “images” can also wrap the data in an Apple disk image container; restoring that container may not reproduce
boot sectors correctly. Using dd directly from /dev/rdiskX creates a true raw sector copy
(bootloader + partitions + files), which is what you want for a bootable clone of the original SD card.
File extension note: we used master.dmg as the filename, but it is actually a raw image when created via dd.
The extension does not change the bytes.
3) Create the master raw image from the ORIGINAL SD
Goal
Create a master image file on your external drive (example: /Volumes/YourName/master.dmg).
Step 3.1 — Insert the ORIGINAL working SD
If macOS shows “disk not readable,” click Ignore (do not initialize). This often happens because macOS can’t read Linux partitions.
Step 3.2 — Identify the disk number
Run:
diskutil list
Find your SD card under something like /dev/disk4 (external, physical).
Use the size to confirm (example: ~53.7GB for the original).
Step 3.3 — Unmount the entire disk
diskutil unmountDisk /dev/diskX
Replace diskX with the SD disk number you found (e.g., disk4).
You want: Unmount of all volumes on diskX was successful
Step 3.4 — Create the raw master image with dd
Choose a destination path on your external HDD/SSD. In our case, the external drive was mounted as
/Volumes/MyName and the file was master.dmg.
sudo dd if=/dev/rdiskX of=/Volumes/Riccardo/r36s_master.dmg bs=4m status=progressNotes:
-
/dev/rdiskXwhere X is the device number (here, X is 4), is the “raw” device (faster than/dev/diskX). - You will be prompted for your Mac password (nothing will show while you type). Press Enter.
- Let it finish completely; don’t interrupt.
Step 3.5 — Eject the ORIGINAL SD safely
diskutil eject /dev/diskXRemember the X here is probably something like 4. Now remove the original SD and store it somewhere safe.
4) Clone the master image to a NEW SD
Goal
Write the master image onto your new SD so it boots exactly like the original.
Step 4.1 — Insert the NEW SD card
If macOS says “disk not readable,” click Ignore. (You may see this even before writing, depending on current formatting.)
Step 4.2 — Identify the NEW SD disk number
diskutil listConfirm the new SD by size (example: ~63.9GB for a “64GB” card).
Step 4.3 — Unmount the NEW SD
diskutil unmountDisk /dev/diskYStep 4.4 — Write the master image to the NEW SD
sudo dd if=/Volumes/YourName/master.dmg of=/dev/rdiskY bs=4m status=progressHere, if you use only one SD-card port on the computer, X will be the same as Y.
Double-check:
-
if=points to your image file on the external drive -
of=points to the NEW SD card raw device (/dev/rdiskY) - Do NOT write to
/dev/rdisk0
Step 4.5 — Eject the NEW SD
diskutil eject /dev/diskYStep 4.6 — Boot test
Insert the new SD into the R36S and power on. It should boot like the original.
5) Repeat for additional SD cards
Yes — you can do this one card at a time in the same reader:
- Insert next blank SD
-
diskutil list(confirm disk number) diskutil unmountDisk /dev/diskYsudo dd if=/Volumes/YourName/master.dmg of=/dev/rdiskY bs=4m status=progressdiskutil eject /dev/diskY
6) Verify + expected macOS popups
“Disk not readable” popup is normal
Your R36S card typically contains a Linux/ext4 partition that macOS can’t read, so macOS may show the popup. Click Ignore.
Check what mounted in Finder
You should typically see mountable partitions like BOOT (FAT32) and EASYROMS (often NTFS/exFAT).
You can also check via Terminal:
ls /Volumes7) Notes: partitions, saves, and extra space
Saves and save states
Saves are not stored “inside the ROM.” They are separate files on the user partition (often EASYROMS).
A full-disk clone copies ROMs, saves, states, configs — everything.
Extra free space on larger SD cards
If you clone a ~53.7GB card onto a ~63.9GB card, the remaining space will typically show as unallocated until you expand the last partition. This is optional and can be done later.
Recommended workflow
- Keep your original SD as a known-good source.
- Keep the master image on your external drive.
- Clone new cards from the master image whenever needed.
Done. You now have a reproducible “master image → clone” workflow for R36S microSD longevity.
Make sure to customize your system by changing the Custom Boot Screen!
