Differences between SDXC and SDHC?

Question

My cohorts and I in the Rockbox project read with interest the announcement on the recent CES of the new SDXC standard for Secure Digital, but we were a little puzzled by the technical differences between the SDHC standard and the new SDXC.

As we understand it, there are no technical limitations in the SDHC that prevent card sizes larger than 32 GB. The only limit is artificial (i.e., recorded in the standard). The technical limit of SDHC is the same as declared as the official limit for SDXC, which is 2 TB.

Is SDXC an official ratification of SDHC beyond 32 GB, or is it actually a completely different implementation?

We strive to ensure that our SD drivers can read and write to these new cards, but it’s difficult to find detailed information about the standard at the moment (without signing an NDA with an SD organization, I’m not going to do it anyway).

Answer 1

From everything that I read (and no, I am not attached to any information covered by the NDA), it looks incompatible at the HW level.

Clearly, the Word of God says nothing more than "nya-nya, you need all new devices to use SDXC!" IMHO

Answer 2

Many devices list a maximum size of 32 GB memory cards based on SDHC specifications, while some devices work with 64-bit SDXC cards in practice, although they may need to be reformatted to FAT32 (used on SDHC) instead of exFAT (used on SDXC format, native format). I base this on a Wikipedia Secure Digital article.

An example of devices that appear to be compatible with SDHC but which accept 64-inch SDXC cards are also some Android smartphones .

The difference seems to be based on software. An SDHC-compatible device can work with SDXC cards if the device’s OS can handle volumes larger than 32 GB and you may need to reformat the SDXC card to FAT32.