The SDHC Specifications sets a minimum guaranteed speed of 2, 4, 6 or 10MB/s to match a host device. This speed rating is commonly referred to as Class 2, Class 4, Class 6 and Class 10 speed.
This rating system was introduced to satisfy the needs of High Definition digital cameras and camcorders, where a guaranteed continuous write speed is more important than the maximum write speed which is affected by many variables.
When using a camera there are some housekeeping rules that can help speed:
- Format the card in the host device (after backing up files)
- Do not try and fill the card to the maximum - as the card gets full it can slow down as the controller needs to find empty space on the card
- If your device asks for a minimum Class 4 memory card use Class 4 or above and you should not encounter any problems
- If the device requires a Class 6 card you can use a Class 6 or a Class 10 card in most cases.
- If the device requires a Class 10 card - You should use a Class 10 card to enjoy the best performance.