The categories of SD flash memory cards 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 Default and High Speed bus. See
SD Card and
SD Express.
Bus Bus Speed
Interface (MB/sec)
Default 12.5
High Speed 25
UHS I 104
UHS II 312
UHS III 624
SD Express 985 (Gen 3x1 lane)
SD Express 1970 (Gen 3x2 lane)
SD Express 3940 (Gen 4x2 lane)
Max. Video
Speed Class Resolution
C6 Default HD
C10 High-speed HD
UHS Speed Class (2010)
U1 UHS-I/II/III HD
U3 UHS-I/II/III 4K
Video Speed Class (2016)
V6 UHS-I/II/III HD
V10 UHS-I/II/III 4K
V30 UHS-I/II/III 4K
V60 UHS-II/III 8K
V90 UHS-II/III 8K
Speed Class Markers
C, U and V designate the speed class, while 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.)