SD card classes designate the minimum write speed of the flash memory card for recording video. The three class types are Speed, UHS Speed and Video Speed. Devices that support any of the UHS buses also support the earlier Normal and High-speed buses. See
SD Card and
SD Express.
MINIMUM WRITE SPEED
Min.
Bus Type Write Highest
MB/sec Recording
Speed Class
C6 Normal 6 HD
C10 High-speed 10 HD
UHS Speed Class (2010)
U1 UHS-I/II/III 10 HD
U3 UHS-I/II/III 30 4K
Video Speed Class (2016)
V6 UHS-I/II/III 6 HD
V10 UHS-I/II/III 10 4K
V30 UHS-I/II/III 30 4K
V60 UHS-II/III 60 8K
V90 UHS-II/III 90 8K
MAXIMUM SPEED
Max.
Bus Type MB/sec
Normal 25
UHS I 104
UHS II 312
UHS III 624
SD Express 985
Speed Class Markers
The C, U and V designate the speed class, while the Roman numerals are the bus type. (Images courtesy of SD Association and SanDisk Corporation.)
More Pins
Starting with the UHS-II bus, the cards have a second row of pins. (Image courtesy of SD Association.)