I did one the other day using a 64GB Thumb/Flash drive and found that Windows forced FAT32 partitioning/formatting at only 32GB but the remaining 32GB couldn't be dealt with in Windows Disk Management, had to boot to a GPARTED LiveCD to clean things up. It's simply a limit of Windows, put a new 64GB MicroSD in my Dell Venue 8 as Drive D for storage and it is formatted as exFAT, works just fine.