SD Cards – No Fluff Consumer Guide
USES
SD cards are used for recording/storing/transporting data in a small format.
TYPES
The most common cards available today are SD, SDHC, SDXC. SDUC is an up-coming technology not in common usage by end-consumers currently. They are available in both standard (normally used in cameras) and micro formats (normally used in mobile/smart phones that provide expandable storage). Micro SD cards can be used in SD card-size converters, allowing them to be used in full-size SD card readers.
DECIDING WHICH SD CARD TO BUY
When it comes to picking the right card for your device, check the compatibility of your device with the cards types available, and decide based on price/storage size/speed ratio depending on your requirements. While not all devices support each size-bracket/speed, if a device can read a newer card formats, it should be able to read the earlier card formats – features will be capped to the speed of the slowest part of the chain.
Fast writes?
If you will need your SD card to store a lot of data quickly (e.g, high-megapixel, burst-mode photography; or HD/4K/8K video), you will want to aim for a faster write speed. If you will be writing a lot of data in photo/video formats you may want to consider a larger storage size as well. Buying more cards at a smaller size may be more economical but you will need to swap the cards more frequently when capacity is used.
Storage size?
If speed isn’t an issue or you will only be writing once or rarely (e.g. if you will be storing MP3’s or videos on the card for playback) you may be able to save money by buying a card with a slower write speed but with a higher capacity.
STORAGE SIZES
| Type | Default Format | Size | |
| SD | FAT12/FAT16 | 128MB – 2GB | |
| SDHC (High Capacity) | FAT32 | 4GB – 32GB | |
| SDXC (Extended Capacity) | exFAT | 64GB – 2TB | |
| SDUC (Ultra Capacity) | exFAT | 2TB – 128TB |
SPEED
While advertised write speeds may be slightly faster than the real-world speeds achieved in normal usage (e.g. due to file fragmentation), they can be a useful guide for the kind of speeds you might expect. The SD Association has tried to make things easier with different class names, but this might still be confusing for some. Write speeds will normally always be slower than read speeds.
Speed Classes
| Speed Class | Icon | Minimal Sequential Write Speed |
| Normal | Number inside a C | Number (2,4,6,8,10) indicates MB/s |
| UHS (Ultra High Speed) | Number inside a U | Number (1,3) indicates 10’s of MB/s |
| Video | V followed by a number | Number (6,10,30,60,90) indicates MB/s |
| Speed MB/s | Normal | UHS | Video |
| 2 | C2 | ||
| 4 | C4 | ||
| 6 | C6 | V6 | |
| 8 | C8 | ||
| 10 | C10 | U1 | V10 |
| 30 | U3 | V30 | |
| 60 | V60 | ||
| 90 | V90 |
Theoretically C6 and V6 are the same write speed; C10, U1 and V10 as also the same; and U3 and V30.
8K video recording should be stable on a V90 SDXC card; 4K video on a V60; HD video on a V30.
Depending on the frames-per-second in burst mode a U3/V30 write speed should suffice for most full frame cameras. If the SD card write speed is too slow you may find the re-take speed suffers as the camera isn’t able to move enough data from its own buffers to the SD card.