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SD Card TOP > SD Memory (Industrial Use) > Speed Class and Performance
| 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.
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.)
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 |  |
Normal Bus I/F | SD video recording |
  |
HD — Full HD video recording | ||
 |
High Speed Bus I/F | Full HD video recording HD still consecutive shooting |
|
| UHS Speed Class |  |
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.
