If your camcorder supports SDXC, what cards you should buy: SDHC or SDXC? The answer may seem obvious: of course SDXC, because they are newer and as such better. But what exactly is better about them?
* Old school SD cards (SD 1.0, SDSC) use FAT file system. It is old, free, reasonably fast. Capacity is limited to 2 GB I believe.
* SDHC cards use FAT32, it is free, reasonably fast, capacity is limited to 2TB (not bad), but max file size is limited to only 4GB (this is why AVCHD files are 4GB max (on Pana) or even 2 GB (on Canon, supposedly because of twice smaller cluster size).
* SDXC cards use exFAT, it is not free, therefore either camcorder manufacturers or card manufacturers or both, I haven't figured that out, have to pay royalties to Microsoft for usage of this patented file system. And because it is patented, you cannot get it for free in Linux distros. Capacity is limited to... some really huge number :-). The allocation table is more complex, hence it may take more time to write to the card (this is my own theory).
Then comes speed rating. It is not directly related to card being SDHC or SDHC. It is possible to have an SDHC card with U-rating (like UHS-I), it is also totally possible to have an SDXC card without U-rating rating.
And it may turn out that older SDHC cards are faster than SDXC. This is not important when you shoot, but it may take you three to five times longer to dump content of a slow SDXC card than of a fast U-rated SDHC card, provided that you have fast USB3 reader.
Here are some tests to prove the point.
This is a test of the ADATA Premier Pro 32GB SDHC UHS-1 Memory Card. The card is rated at 95MB/s read and 45MB/s write. Reader used: Transcend TS-RDF8K (USB 3.0).
This is a test using the same reader. Only SDXC cards in the test. UHS-I rated Patriot LX is 60% faster than a Class 10 card. Still, the 30 MB/s SanDisk card (SanDisk seem to have deep disdain to C- and U- ratings) is even faster, still "only" at 40 MB/s.
Finally, a Polish test using the same reader. They used a fast SDHC card (they say it is rated to 80 MB/s, sadly they did not provide the model or class) and a slower SDXC card (again, no model or rating, but as you can see, SDXC cards can be slow!) The difference is 3:1 or read and about 2.5 : 1 on write. They used 11 large files, total about 15GB.
* Buy SDXC cards only if you really-really-really need more than 32 GB of storage per card. Do you? I don't. Most of my cards are still 4 GB, they dump nicely to a recordable DVD, although I bought a couple of 16 GB recently.
* If you shoot a lot of videos or photos and you cannot wait for the files to copy from card to your computer, consider buying a USB3 reader (you need support for USB3 on the computer) and look for U-rated cards. AFAIK
, the only class available for now is UHS-I. As these tests show, these cards are at least twice faster for dumping files onto computer than Class 10 cards.
* If you buy SDXC cards make sure they are U-rated. But you can see from the tests, that even UHS-I SDXC cards are about twice slower than UHS-I SDHC cards. I think this is where the exFAT overhead shows its ugly head. Or tail. Or the whole ugly body.
Anyway, as for me personally, I will be buying SDHC cards only for forseeble future. I need to check with my cameras (I have multiple). The Canon HF100 won't take Class 10 cards without firmware update, and I don't know whether it will ever take UHS-I. The 2008 HDC-SD9 has no problems with Class 10 cards, I need to try it with a UHS-I card. I sold the HMC40... Oh, the Nikon D3200, need to check it with a UHS-I card as well.
Need to get myself a fast reader too.