|| What is class speed rating on a SDHC memory card and what does the class 2 ,class 4 and class 6 really mean?
| The simple answer is that SDHC cards are defined by one of three “classes” that allow the user to best understand performance capabilities. The class rating of SDHC cards specifies a minimum sustained write speed.
SDHC Class 2: 2MB/sec
SDHC Class 4: 4MB/sec
SDHC Class 6: 6MB/sec
Even though the physical form factor of an SDHC card is identical to the form factor of a standard SD card, the new cards can be identified by the SDHC logo appearing on both the card packaging and the label. Unless you see the SDHC logo, then it’s best to assume that the card is in the standard SD format.
SDHC cards will usually advertise a maximum speed (such as 80x or 150x) in addition to this minimum Speed Class Rating. One critical difference between the Speed Class and the maximum speed ratings is the ability of the host device to query the SD card for the speed class and determine the best location to store data that meets the performance required.
Sometimes a class 4 SDHC card will out perform a class 6 SDHC card in your device because it may have a higher max speed and you device can make good use of it due to good compatibility between the two.
If you want to be safe you should go by the SDHC class rating on the package. If you want the fastest performance with your device check around and look on forums to see if your new camcorder and make use of that 150x speed rating.
“Maximum speed” ratings are unofficial and have no formal evaluation process.