A microSD card is a small removable flash memory card measuring about 15 by 11 mm, used in phones, action cameras, drones, handheld consoles, and single-board computers. It uses NAND flash and is the smallest common form of the SD standard.
Why it matters
Capacity classes affect compatibility. SDHC covers up to 32 GB, SDXC up to 2 TB, and SDUC beyond that. Older devices may not read larger cards, and the file system matters: FAT32 is limited to 4 GB files, while exFAT handles large video files.
Speed labels are confusing but useful:
- Speed class (C10) and UHS class (U1, U3) give minimum sustained write speeds.
- Video class (V30 and others) shows sustained video recording speed.
- Application class (A1, A2) indicates random read/write performance for running apps.
Cheap cards and counterfeits are common, and they can fail silently.
Example
Recording 4K video on an action camera usually calls for a U3 or V30 card. A Raspberry Pi running its operating system from a card benefits from an A1 or A2 card, because many small random reads and writes affect responsiveness.
Common mistakes
- Judging a card only by its headline read speed.
- Buying from unreliable sellers and not testing capacity.
- Pulling the card out while it is being written.
- Using a card as the only copy of important photos.
Related
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