Quick answer: Throw away the card that came with the handheld and buy a name-brand card from SanDisk or Samsung. A SanDisk Ultra 128 GB (A1) is plenty for a Miyoo Mini Plus or an Anbernic XX-series handheld; a faster A2 card such as the SanDisk Extreme suits an Android handheld like the Retroid Pocket. Format it the way your firmware expects: FAT32 for Onion OS on the Miyoo (the Onion team says “not exFAT”), exFAT for the ROM card on most Anbernic firmware and for Android handhelds. Buy from a reputable seller, because fake high-capacity cards are common.
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This guide is based on the official Onion OS installation guide, Retro Handhelds’ Anbernic XX starter guide, Retroid’s product page and the SD Association’s definitions of speed classes. Card speeds are the makers’ published figures, not our own benchmarks.
Why replace the card that came with your handheld?
Both the Onion OS team and Retro Handhelds tell you to do it first. The Onion guide says the card included with the Miyoo Mini “is known to be slow, and will likely ruin your experience and/or data”, and recommends reputable brands, naming SanDisk and Samsung. Retro Handhelds says the generic cards supplied with Anbernic’s XX handhelds “are prone to failure and do not last very long”. A card failure means lost saves, so copy your save folder off the stock card before you swap.
Card size and format by device
| Handheld and firmware | Card slots | File system | Suggested size |
|---|---|---|---|
| Miyoo Mini and Mini Plus (Onion OS) | One | FAT32 with MBR (Onion: “not exFAT”) | 64 to 128 GB |
| Anbernic XX series, stock firmware | Two: TF1 system, TF2 games | TF1 is written from the firmware image; on TF2 you just make ROMs and BIOS folders | Retro Handhelds: stock firmware needs a 64 GB TF1 card |
| Anbernic XX series, custom firmware (muOS, Knulli, MinUI) | Two | Varies: MinUI wants FAT32 on TF2, Knulli uses EXT4 | 32 GB TF1 plus 64 GB or larger TF2 (Retro Handhelds) |
| Retroid Pocket (Android) | Internal storage plus one microSD | Android formats it when you set it up (usually exFAT) | 128 to 256 GB, more for disc-based systems |
Miyoo Mini Plus: FAT32, and how to format a large card
Windows will not format cards over 32 GB as FAT32 with its own tools. The Onion guide says to use Rufus: choose the card, set Boot selection to “Non bootable”, keep the partition scheme as MBR, set the file system to “Large FAT32” and use a 32 KB cluster size (it notes 16 KB “might extend the life” of the card). It also warns against GUIFormat and fat32format because “many users are reporting file system errors on cards above 128 GB”. On a Mac, Disk Utility’s MS-DOS (FAT) with Master Boot Record does the job.
Anbernic XX series: two cards
Anbernic’s RG35XX-family handhelds have two slots. TF1 holds the operating system and TF2 holds your games. Retro Handhelds recommends a 32 GB card for a custom firmware on TF1 and at least 64 GB for TF2, or a 64 GB TF1 card if you stay on Anbernic’s stock firmware. Retro Handhelds writes the firmware to TF1 with balenaEtcher, which sets the format for you. TF2 depends on the firmware: on stock firmware you just create ROMs and BIOS folders; MinUI wants TF2 formatted FAT32; Knulli switches the second card to EXT4, which Windows and macOS cannot write to without extra tools, so you copy games over the network or from a Linux machine; muOS has its own wiki guide.
Retroid Pocket: Android handles it
The Retroid Pocket 5 has 128 GB of internal UFS 3.1 storage plus a microSD slot. As an Android device it formats a new card when you set it up, normally as exFAT, which has no 4 GB file-size limit. That matters for larger disc images: FAT32 cannot store a single file over 4 GB. Because Android emulators load games and apps from the card, an A2 card is the better buy here.
What the labels on the card mean
The SD Association sets these ratings:
| Label | Minimum guaranteed by the SD Association | Matters for |
|---|---|---|
| U1 / Class 10 | 10 MB/s sustained write | Basic use; fine for small cartridge-era games |
| U3 / V30 | 30 MB/s sustained write | Faster copying of large libraries |
| A1 | 1,500 read IOPS, 500 write IOPS | Linux handhelds loading small files |
| A2 | 4,000 read IOPS, 2,000 write IOPS | Android handhelds running apps from the card |
Sources: SD Association, Application Performance Class and Speed Class. The big “up to 190 MB/s” read figures on packaging are best-case numbers and often need a matching card reader.
Recommended cards
| Card | Published ratings | Best for |
|---|---|---|
| SanDisk Ultra 128 GB | Up to 140 MB/s read, U1, A1 | Miyoo Mini Plus, Anbernic XX TF2 |
| SanDisk Extreme 256 GB | Up to 190 MB/s read, 130 MB/s write, U3, V30, A2 | Retroid Pocket and other Android handhelds |
| Samsung EVO Select or PRO Plus | See Samsung’s listing for the current model’s ratings | Good alternative; we did not find a current Amazon US offer to link today |
- SanDisk Ultra 128 GB microSDXC (A1): check current price.
- SanDisk Extreme 256 GB microSDXC (A2, V30): check current price.
How to spot a fake card
Fake cards report a large capacity but store far less, and they corrupt files once the real capacity is full. Buy from the brand’s own store or a listing “sold by” the retailer rather than an unknown marketplace seller, be wary of prices far below the norm, and test a new card with a full-capacity checker such as H2testw (Windows) or F3 (Mac and Linux) before you copy your library onto it.
What to put on the card
Each firmware has its own folder layout for BIOS files and games, so follow its guide. Only use game files you have the right to use, such as backups of cartridges and discs you own, and homebrew.
Related guides
- Anbernic vs Miyoo vs Retroid: which brand to choose
- Best retro gaming handhelds under $300
- Best replacement batteries for retro handhelds
- Retro gaming handhelds on Amazon UK
Sources: Onion OS: Fresh install; Retro Handhelds: Anbernic XX handheld starter guide; Retroid Pocket 5 product page; SD Association Application Performance Class and Speed Class; SanDisk and Samsung product listings.
FAQ
What is the best SD card for a Miyoo Mini Plus?
A name-brand card such as a SanDisk Ultra 64 or 128 GB, formatted FAT32 with MBR. The Onion OS guide warns that the stock card is slow and recommends SanDisk or Samsung.
Should I format my handheld SD card as FAT32 or exFAT?
Follow your firmware. Onion OS on the Miyoo needs FAT32, not exFAT. Android handhelds such as the Retroid Pocket use exFAT. Anbernic ROM cards depend on the firmware you run.
Do I need an A2 SD card for a retro handheld?
Not for Linux handhelds like the Miyoo or Anbernic XX series, where A1 is fine. A2 helps on Android handhelds that run apps and emulators from the card.
What size SD card do I need for an Anbernic RG35XX?
Retro Handhelds suggests a 32 GB card for custom firmware plus a 64 GB or larger card for games, or a 64 GB system card if you keep Anbernic’s stock firmware.
Why should I replace the SD card that came with my handheld?
The supplied cards are generic and, according to the Onion team and Retro Handhelds, slow and prone to failure. Back up your saves and move to a name-brand card.