I didn't think the Evo 3D could handle anything bigger than 32GB.
Original SD cards (SD standard capacity or SDSC) could only go up to 2GB. That's why a lot of older stuff can't handle anything bigger than 2GB.
High capacity SD (SDHC) goes up to 32GB. That's why most phones specs specify expanable up to 32GB or something like that.
SDXC (extended capacity) goes up to 2TB. I'm surprised that the Evo 3D plays nice with an 64GB SDXC card.
Edit: just did a little research and found this... (swiped from wikipedia)
SDHC host devices will accept SDXC cards that follow Version 3.0, since the interface is identical,[3] but the following issues may affect usability:
*SDXC cards are pre-formatted with Microsoft's proprietary and patented exFAT file system, which the host device might not support. Since Microsoft does not publish the specifications of exFAT and its use requires a non-free license, many alternative or older operating systems do not support exFAT for technical or legal reasons. The use of exFAT on some SDXC cards may render SDXC unsuitable as a universal exchange medium, as an SDXC card that uses exFAT would not be usable in all host devices. Since the FAT32 file system supports volumes up to the SDXC's maximum theoretical capacity of 2 TB as well, a user could reformat an SDXC card to use FAT32 for greater portability between computers (see below). FAT32-formatted SDXC cards can be used in a host device built for SDHC if the host device can handle 64GB and larger volumes.
*SDHC host devices will not test the new capability bits defined for SDXC 4.0 cards. It will therefore not be able to use the new features of SDXC, such as transfer speeds above UHS104 (104MB/s).
(from
Secure Digital - Wikipedia, the free encyclopedia )