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SD Memory (Industrial Use)
Speed Class and Performance

1. Speed Specification and Performance of SD Memory Cards

Bus Interface Standard Conventional UHS-I
Mode HS DDR50 SDR50 SDR104
Signal Amplitude 3.3 V Amplitude 1.8 V Amplitude
Clock Frequency 50 MHz 50 MHz 100 MHz 208 MHz
Data Frequency 50 MHz 100 MHz 100 MHz 208 MHz
Logic Performance 104 MB/s
(Bus Speed)
25 MB/s 50 MB/s 50 MB/s 104 MB/s

What is UHS-I ?

UHS-I (Ultra High Speed I) is a speed specification for SD Memory Cards that was established in 2010. Its features include a maximum bus interface speed of up to 104 MB/s. It utilizes conventional SD design assests and offers enhanced speeds. Three different modes (DDR50, SDR50 and SDR104) have been standardized for the UHS-I based on the application and objective.

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 minimum writing performance. It was designed for streaming data recording.The "Speed Class", Class2, 4, 6 and 10 for the current Bus I/F and the "UHS Speed Class" Class 1 works under UHS-I Bus I/F. (The Speed Class and the UHS Speed Class are not compatible.)

Marks Operable under... Applications
Speed Class CLASS 2 Normal Bus I/F SD video recording
CLASS 4CLASS 6 HD — Full HD video recording
CLASS 10 High Speed Bus I/F Full HD video recording
HD still consecutive shooting
UHS Speed Class UHS-I UHS-I Bus I/F For higher potential of recording real-time broadcasts and capturing large size HD videos

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.