Technical Information about SDHC™ memory cards
With the new SD v2.00 specifications, all the SD memory cards above 2 GB have to be SDHC.
The SDHC memory cards only works with SDHC digital appliances.
The new format also includes the Speed Class.
Speed Class 2: 2Mo/s minimum
Speed Class 4: 4Mo/s minimum
3.4 Speed Class
Four Speed Classes are defined and indicate minimum performance of the cards
- Class 0 – These class cards do not specify performance. It includes all the legacy cards prior to this specification, regardless of its performance
- Class 2 – Are more than or equal to 2MB/sec performance.
- Class 4 – Are more than or equal to 4MB/sec performance.
- Class 6 – Are more than or equal to 6MB/sec performance.
High capacity SD Memory Cards shall support Speed Class Specification and have performance more than or equal to Class 2.
Note that the unit of performance [MB/sec] indicates 1000x1000 [Bytes/sec] while the unit of data size [MB] indicates 1024x1024 [Byte]. This is because the maximum SD Bus speed is specified by the maximum SD clock frequency (25 [MB/sec] = 25000000 [Bytes/sec] at 50 MHz) and data size is based on memory boundary (power of 2).
Speed Class 6: 6Mo/s minimum
