The SD Card Association has defined four speed fraction levels

  • Normal speed grade: C2, C4, C6, C10
  • UHS speed grade: U1, U3
  • Video speed grade: V6, V10, V30, V90
  • Application performance level: A1, A2

1. Class grade standard (normal speed grade)

C0-C10 markings on memory cards

Early memory card speed grade using Class grade to identify. There are mainly C10, C6, C4 and C2 markings. C1 represents CLASS1, C10 represents CLASS10, and the number corresponding to C is equivalent to the corresponding number of CLASS.

  • C2 has a minimum write speed of 2MB/sec and is a low-speed memory card, suitable only for small-capacity storage documents;
  • C4 minimum write speed of 4MB/sec;
  • C6 has a minimum write speed of 6MB/sec;
  • C10 minimum write speed of 10MB/sec, belongs to the entry can be used for digital expansion, digital cameras, audio and video playback, but 4K continuous shooting or HD camera continuous recording, car recorder continuous shooting, not recommended.

2. UHS Grade Standard (Ultra High Speed Grade)

Memory card marked with U1, U3 logo

UHS (Ultra High Speed) ultra-high speed grade is a new bus mode. Currently there are three versions of UHS-I, UHS-II and UHS-III. To achieve the UHS standard transmission speed requires device support, the higher version is backward compatible with the lower version, does not support the standard can be compatible with the speed reduction for ordinary memory card use.

Daily use of U1 (minimum write speed 10M/S) and U3 (minimum write speed 30M/S) levels identify the minimum write speed.

  • UHS-I cards have a maximum read speed of 104M/S;
  • UHS-II cards have a maximum read speed of 312M/S;
  • UHS-III cards have a maximum read of 624M/S.

3. VSC grade standard (video speed grade)

Memory card marked with V6, V10, V30, V60, V90 logo.

Video Speed Class Video Speed Class, 4K video shooting demand increased, the SD Association for video shooting applications to develop the video speed class, to identify the letter V plus the minimum write speed value of the number constitutes the logo.

  • V6 read/write speed is approximately equal to 6M/sec, V10 is approximately equal to 10M/sec, and so on.
  • V10 minimum write speed 10M/s, performance equivalent to C10, U1 belongs to the entry card.
  • V30 minimum write speed of 30M/s, basically can be to everyone’s use requirements, in camera video, car recorder use.
  • V60 minimum write speed of 60M/s.
  • v90 minimum write speed of 90M/s.

4K shooting generally need V30 or V60 grade memory card, 8K photography with V90.

4. Application performance level

Memory cards are marked with A1 and A2 logos

A1 and A2 logo certification full name is Application Performance Class 1 and Application Performance Class 2 (i.e. application performance class 1 or 2), more in line with the expansion of Android and other systems and application use requirements.

  • A1 Read and write capability 1500 Read IOPS (random reads), 500 Write IOPS (random writes);
  • A2 read and write capability 4000 Read IOPS (random read), 2000 Write IOPS (random write).

Read and write speed A1, A2 level of minimum performance requirements is 10MB / s. But for applications in smart devices with systems using A2 is more suitable.