Cheap storage with conditions attached
Memory cards have quietly changed role. They used to be where apps went when the phone filled up; they are now essentially a media drive. Android has steadily restricted what removable storage can hold, most manufacturers dropped the feature that let a card be adopted as internal storage, and apps themselves almost never move any more.
That leaves a card doing one job very well and cheaply: photographs, video, music, downloads and backups. The conditions attached are that cards are counterfeited on a large scale, they wear out without warning, and the way you format one determines whether the files on it can be read anywhere else.
What a card can hold, and what it cannot
| Content | On a card? | Notes |
|---|---|---|
| Photographs and video | Yes, ideally | Point the camera app at the card in its settings |
| Music and podcasts | Yes | Most players let you choose the download location |
| Downloads and documents | Yes | Move them with a file manager, not by copying twice |
| Films for a flight | Yes | The best single use of a card |
| Apps | Rarely, and rarely well | Most cannot move, and those that do load slower |
| Game data and large assets | Almost never | Modern games keep assets in internal storage |
| Anything you cannot lose | No | Not without a second copy elsewhere |
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Buying a card that is what it claims to be
- Match the class to the job, not the biggest number For video recording, a V30 rating means sustained write speed. For general storage, A1 or A2 indicates it handles small random reads reasonably. Bus speed markings describe the ceiling, not the floor.
- Buy from somewhere with a returns process Counterfeit cards are widespread on open marketplaces. A fake typically reports a large capacity and holds a fraction of it, discarding everything written past the real limit.
- Test the whole card before trusting it A write-and-verify test fills the card and reads it back. It takes an hour or two and it is the only way to catch a fake before it eats a holiday's photographs.
- Check the reported size against the packaging A genuine card shows slightly less than its advertised capacity. A fake often shows exactly the round number, or more than the box claims.
- Format it in the phone that will use it This gives the right filesystem and alignment. Cards above thirty-two gigabytes will normally end up as exFAT, which modern computers read without extra software.
- Label what is on it A card is going to end up in a drawer with four others. Thirty seconds with a marker saves an afternoon later.
SD Card Test. Writes across the whole card and reads it back to verify it. This is the test that exposes a counterfeit, and it is worth the wait on a new card.
SD Insight. Reads the card's own manufacturer identifier rather than the label printed on it, which frequently disagrees with what the packaging claimed.
DiskInfo. Reports real capacity, filesystem and mount points for internal and removable storage in one place.
Storage Analyzer. A visual map of what is filling both the phone and the card, which is how you find the one folder responsible for most of it.
Solid Explorer. The most capable file manager for moving folders between internal storage and a card, with a two-pane view and proper handling of the permission Android asks for.
Total Commander. Tiny, fast and unfashionable, with the best bulk operations of any file manager here.
Material Files. Clean, open source and free, and enough for moving media around without advertising.
MiXplorer. The power user's choice: archives, network shares and batch renaming, distributed outside the Play Store.
Files by Google. Its move-to-SD-card suggestion is the easiest safe way to shift photographs and downloads for someone who does not want a file manager.
SD Maid SE. Finds the folders left behind by uninstalled apps, on both internal storage and the card. Read what it proposes before letting it delete.
DiskDigger. Photo recovery for a card that has been formatted or corrupted. Stop writing to the card first; every new file reduces what can be recovered.
Syncthing. Copies the card's contents to a computer whenever both are on the same network, which is the backup that makes a card failure an inconvenience rather than a loss.
When the card starts to fail
Cards fail in a recognisable pattern: photographs that will not open, files that reappear after deletion, the phone reporting the card as damaged and offering to format it, and the card disappearing and returning at random. These are symptoms of the card, not the phone, and they get worse rather than better.
The response is the same in each case. Stop writing to it immediately, take it out, and read it in a computer with a card reader if you can. Copy everything readable off before attempting any repair, because a format or a filesystem fix can succeed at making the card usable while destroying what was on it. Recovery tools work best on a card nothing has written to since the problem began.
- Photographs and video, with a backup
- Films and music for a journey
- Downloads and documents
- Moving large files to a computer
- The only copy of anything
- Apps and game data
- Constant small writes from a busy app
- Long term archival storage
The habits that stop this being a problem
Point the camera app at the card from the start, so photographs go there rather than being moved later. Set one automatic copy to somewhere else, whether that is a cloud service or a computer on the home network, because a card with no second copy is a countdown. And replace the card every few years rather than waiting for the first corrupted file, since they are cheap and the alternative is not.
Before a factory reset or a new phone, take the card out first. A portable-formatted card slots straight into the next phone with everything intact, which is the nicest property it has and the one people forget at exactly the wrong moment.
Format as portable, test a new card before trusting it, keep media on it and apps off it, and never let it hold the only copy of anything.
Frequently asked questions
Can I still move apps to an SD card?
On most modern phones, no. The move option has disappeared from all but a few apps, and where it exists it usually moves only part of the app. Treat a card as media storage and plan internal storage for apps.
What is the difference between formatting as portable and as internal?
Portable makes it a removable drive readable in other devices. Internal encrypts it and binds it to that phone, so it cannot be read anywhere else and is lost if the phone fails. Most manufacturers have removed the internal option; where it exists, portable is still the safer choice.
How do I know whether a card is counterfeit?
Run a full write-and-verify test on it before use. A fake reports a capacity it does not have and silently discards data written beyond its real size, so the files appear to copy successfully and are empty when you come back to them.
The phone says the card is damaged and wants to format it. Should I?
Not before trying to read it in a computer with a card reader and copying off whatever is readable. Formatting makes the card usable again and makes recovery much harder. If nothing can be read anywhere, the card is likely finished regardless.
Why is my phone slower since I added a card?
Usually because something that writes frequently is now writing to slow storage. A cheap card with a low random-write rating is noticeably worse than internal storage; check the class marking and avoid putting anything that writes constantly on it.
Do memory cards wear out?
Yes. They have a finite number of write cycles and no useful warning before failure. That is not a reason to avoid them, only a reason never to keep the single copy of anything on one.
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