this card would not show 64 GB until i spent $60 on a card reader that supports sdxc, and after doing that, it is transferring at class 1 speed. i managed to get it formatted in FAT32 with 59 GB free for my Cowon J3, but it's taking 10 hours to transfer 30 GB to it. i got a refund because this is not the service and quality i paid for. i just hope the music lists on my PMP when i turn it on tomorrow. i have it in the microSDXC slot of the AFT PRO-57U, which is connected to a Syba VIA VL800 USB 3.0 card. feel free to tell me i am doing it wrong and how to get class 10 speed.UPDATE: the transfer finished, but the data does not show in my Cowon J3, so the early versions that worked are gone. do not buy these for a device that is not SDXC specific because they have changed something in them.