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Industrial SD Card
Speed Class and Performance

1. Speed Specification and Performance of SD Memory Cards

Bus Interface Standard Conventional UHS-I UHS-
Mode HS DDR50 SDR50 SDR104 FD156 HD312
Signal Amplitude 3.3 V 1.8 V 0.4 V
Clock Frequency 50 MHz 50 MHz 100 MHz 208 MHz 52 MHz
Logic Performance 104 MB/s
(Bus Speed)
25 MB/s 50 MB/s 50 MB/s 104 MB/s 156 MB/s 312 MB/s
2. Maximum Speed

This means the maximum speed in write or read operations onto SD memory card.
(*The average performance of these operations is lower than the maximum speed and depends on the situation of the inner status of SD memory card.)

3. Speed Class (Guaranteed Minimum Speed)

Speed Class designates the minimum writing performance. This is the performance standard for writing to the card at a constant speed, mainly for data streaming applications such as video recording. Speed Class 2, 4, and 6 (Class 2, 4, and 6) operate in Normal Speed mode, which is the conventional Bus mode, and Speed Class 10 (Class 10) operates in High Speed mode. UHS Speed Class 1 and 3 operate in UHS-I or UHS-II mode. (Speed Class and UHS Speed Class are not compatible.)

Marks Minimum Constant Write Speed* Operable under... Applications
Speed Class CLASS 2 2MB/s (16Mbps) Normal Bus I/F SD video recording
CLASS 4 4MB/s (32Mbps) HD — Full HD video recording
CLASS 6 6MB/s (48Mbps)
CLASS 10 10MB/s (80Mbps) High Speed Bus I/F Full HD video recording
HD still consecutive shooting
UHS Speed Class UHS-I 10MB/s (80Mbps) UHS-Ι Bus I/F
UHS- Bus I/F
For higher potential of recording real-time broadcasts and capturing large size HD videos
UHS-Ⅱ 30MB/s (240Mbps) Shooting 4K2K motion images

* This speed performance is achieved under the conditions specified by the SD Association.

Fragmentation and Speed

Fragmentation and speed are related to the way in which card memory is divided into minimum memory units. Because devices write data into memory locations where none is already stored, the data becomes divided into smaller units, which leads to fragmentation. As fragmentation proceeds, the writing speed is reduced. Speed Class standards help compensate for this fragmentation.