A retro handheld console won't read just any microSD card formatted any old way. Some machines require FAT32 and refuse everything else. Others accept exFAT and are better off for it. Between the two, one difference decides everything: FAT32 caps each file at just under 4 GB, exFAT has no such limit. The rest — allocation unit size, which tool to use, which capacity makes sense — follows from that. Here's how to choose, and how to format cleanly on Windows, macOS and Linux without losing what was on the card.
The trade-off in one sentence
FAT32 is read by everything, including the oldest firmwares, but no file on it can exceed 4 GB. exFAT has no awkward limit, but not every console can mount it.
What FAT32 costs you
The exact limit is 4,294,967,295 bytes, i.e. 4 GB minus one byte. No problem for 8-bit, 16-bit, PlayStation 1 or Nintendo DS. It becomes a blocker as soon as you move up: an uncompressed GameCube or PS2 disc image goes well beyond that threshold, and so do some PSP or Dreamcast files. The copy then fails during transfer, with a message saying the file is too large for the destination file system. The card isn't the problem, the format is.
The second cost: on a large card, opening a folder with several thousand entries is noticeably slower than with exFAT.
What exFAT costs you
Compatibility. The exFAT driver only entered the Linux kernel in version 5.7; many retro consoles run an older kernel, frozen by the manufacturer, and can't mount an exFAT partition. That's the case with the Miyoo Mini: the Onion developers state it in black and white, the machine doesn't support exFAT.
Another point: exFAT has no journal. A power cut during a write leaves an inconsistent file system more often than with a journaled format. Shut down through the menu, never by holding the power button.
Which format for which machine
There's no universal rule: it's the installed firmware, not the console brand, that decides.
| Firmware or machine | Expected format | Practical limit |
|---|---|---|
| Miyoo Mini and Mini Plus (Onion) | FAT32 only | exFAT not supported by the console |
| TrimUI Brick, stock firmware | FAT32 | Above 32 GB, a third-party tool is needed |
| muOS | FAT32 or exFAT, exFAT recommended | Format first with the SD Association tool, to remove hidden partitions |
| KNULLI | exFAT or ext4, via the console's built-in formatter | FAT32 isn't offered; ext4 can't be read from Windows or macOS |
| ArkOS | Games partition in exFAT; second card in ext4, exFAT or NTFS | With ext4, permissions must be adjusted or games won't show up |
| ROCKNIX | FAT32, exFAT, ext4 or btrfs | Merged storage across two cards requires ext4 |
| Android consoles (Retroid, Anbernic Android, AYN) | exFAT | No 4 GB per-file limit |
| Windows consoles (ROG Ally, MSI Claw) | NTFS or exFAT | NTFS for PC games, exFAT if the card moves between machines |
Check what your exact firmware version requires on our firmware compatibility table: custom systems evolve quickly, and advice that was valid a year ago may no longer be.
Capacity: why 512 GB or 1 TB doesn't always make sense
The SD specification already assigns a format to each tier. SDHC cards, from 4 to 32 GB, come formatted in FAT32 from the factory; SDXC cards, from 64 GB to 2 TB, in exFAT. Buying a 512 GB card to reformat it in FAT32 means working against the specification.
On a machine that only accepts FAT32, a very large card brings little: the big files that would justify the capacity exceed 4 GB and won't fit. The 8-bit, 16-bit, PS1 and DS library that a Miyoo Mini Plus or a TrimUI Brick can run fits on 128 or 256 GB. Keep large capacities for Android consoles.
One last point: fake cards advertised as 512 GB or 1 TB for a few euros exist in large numbers. They report a capacity they don't have and silently lose data beyond their real size. That's why we check every microSD card with a full write-and-read-back pass before shipping. If you buy elsewhere, check yours before any transfer. The topic is covered in detail in our guide to choosing a microSD card.
Before formatting: what to back up
Copy to your computer, in a dated folder:
- the game save and save state folders, whose location depends on the firmware;
- the BIOS folder, if you've added any;
- the configuration files you've modified, especially RetroArch's;
- box art, which takes a long time to download again, and your favourites lists when the firmware stores them on the card.
If the card you're formatting is the one supplied with the console, make a full image of the card, not just a copy of the visible files: the boot partition doesn't show up in the file explorer and can't be recreated by hand. Our article on retro handheld console backups details the method for each firmware.
Formatting on Windows
Why File Explorer refuses
Above 32 GB, the File Explorer format window and the Disk Management tool no longer offer FAT32, only exFAT and NTFS. That's Microsoft's decision, not a limit of the format: FAT32 handles up to 2 TB with 512-byte sectors. The format X: /FS:FAT32 /Q command runs into the same refusal and replies that the volume is too big.
In 2026 Microsoft announced, first in the Windows 11 Insider channels, that this limit would be raised to 2 TB on the command line, with the graphical interface keeping the 32 GB cap. Check this against your version: if your format still refuses, use a third-party tool.
The method that works
SD Memory Card Formatter, published by the SD Association, restores the card to the state defined by the SD specification and removes hidden partitions that some manufacturers leave behind. The association recommends its tool over those of the operating system, which aren't optimised for SD cards. However, it doesn't let you choose the format: it applies the one for the card type, so exFAT on an SDXC card. It's the right first pass on a new or temperamental card.
Rufus, free and open source, handles the second pass when you need FAT32 above 32 GB. Select the card in the device list — check three times that it isn't your external drive —, choose “Non bootable” as the boot selection, then FAT32, or “Large FAT32”, which appears for large capacities. The TrimUI Brick and Miyoo Mini installation guides point to this tool.
Formatting on macOS
macOS doesn't have Windows' 32 GB limit. Open Disk Utility, go to View then “Show All Devices”, and select the physical device — the top line, the one with the manufacturer's name — not the volume below it. Click Erase, choose “MS-DOS (FAT)”, which corresponds to FAT32, or “ExFAT”, and leave the scheme on “Master Boot Record”, i.e. MBR.
On the command line, find the identifier with diskutil list, then run sudo diskutil eraseDisk FAT32 NAME MBRFormat /dev/diskN. The volume name must be eleven characters or fewer, in capitals, with no accents or spaces.
Formatting on Linux
Identify the card with lsblk, which shows the capacity of each device: it's the safest check before a destructive command. Then unmount the partition with sudo umount /dev/sdX1.
For FAT32, the tool is mkfs.vfat, provided by the dosfstools package: sudo mkfs.vfat -F 32 -n GAMES /dev/sdX1. The -F 32 forces the 32-bit variant, otherwise FAT16 may be chosen on small cards. For exFAT, install exfatprogs then run sudo mkfs.exfat -n GAMES /dev/sdX1: it's the implementation maintained today, the exfat-utils and exfat-fuse packages are outdated.
If the partition table needs redoing, GParted and the GNOME Disks app do the job graphically.
Allocation unit size
This is the size of the smallest block that can be allocated, also called cluster size. A 3 KB file on a card formatted with 32 KB blocks still takes up 32 KB. Across tens of thousands of small files — box art, saves, 8-bit games — the wasted space becomes noticeable.
Windows' default values are 4 KB for a FAT32 volume from 256 MB to 8 GB, 8 KB from 8 to 16 GB, 16 KB from 16 to 32 GB. With exFAT, 32 KB up to 32 GB, then 128 KB above that.
Leave the default value offered by the tool: it's almost always right. Above all, don't go down to 512 bytes “to save space”; the Onion developers list cards formatted that way that Windows no longer recognised. Don't go up to 64 KB in FAT32 either, a value some machines refuse.
The mistakes that cost you a card, or a weekend
Formatting the original system card
The most common and most costly mistake. On many Linux consoles, the supplied card contains a boot partition that's invisible from Windows. Formatting it leaves the console dead, and the factory firmware can't always be downloaded again in the exact version that was installed. If you have two slots, work on the second one; otherwise, buy a second card before touching anything.
Formatting in NTFS
NTFS is the Windows format. Linux retro consoles don't mount it, or only read-only, which prevents saves from being written. Keep it for Windows handheld consoles.
Formatting from the console
Some firmwares such as KNULLI include their own formatter, and in that case it's the method their developers recommend: it creates the expected partitions and labels. On a firmware that doesn't document this feature, an option hidden in a system menu could just as well reformat the boot card. When in doubt, format from the computer.
Forgetting the volume label
Several firmwares identify their card by its volume name, not by its slot. A field left blank, or a made-up name, gives you a console that boots without seeing its games. Check the expected name in the firmware documentation.
And after formatting
A freshly formatted card is empty: you need to recreate the exact folder structure the firmware expects, with the system names it recognises. That's the subject of our article on the file structure for each firmware. If you're switching systems at the same time, follow our guide to installing custom firmware.
Frequently asked questions
Can I switch from FAT32 to exFAT without losing everything?
No. Changing file system means formatting, and therefore completely erasing the card. Copy everything to your computer, format, then copy it all back. On a well-filled card, the round trip takes hours.
Will my console read a 1 TB card in FAT32?
Technically, FAT32 handles up to 2 TB, and a console that reads FAT32 will often read the card. The benefit is still small: you're stuck at 4 GB per file, browsing slows down, and the machines that require FAT32 run systems with small files. A 128 or 256 GB card is a better fit.
Is a quick format enough, or do you need a full format?
A quick format only rewrites the file system tables and is almost always fine. A full format, which takes longer, goes through every block: keep it for a card that has already shown read errors, or a second-hand card.
Why does my 64 GB card only show 59.4 GB after formatting?
Because the manufacturer counts in decimal gigabytes, one billion bytes, while the system displays gibibytes, i.e. 1,073,741,824 bytes: a difference of about 7%. A small fraction also goes to the file system structures. It's neither a defect nor a counterfeit.
Should you partition the card?
For a games card, a single partition is enough. Multiple partitions only make sense if the firmware requires them, and in that case its installer creates them. Don't create them by hand without explicit instructions.
My computer no longer sees the card after a failed format. What should I do?
Run it through SD Memory Card Formatter again: it writes a clean partition table where an interrupted format left inconsistent structures. If the card stays invisible on two different readers and two different computers, it's probably dead. A card bought from us is covered by the 2-year guarantee: write to us, and we'll replace it.
The format is only one step: what matters next is the card, its speed and its reliability. Ours are grouped in the microSD cards collection.