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By sebmadgwick
What is different about HC SD cards? I had thought (and hoped) that HC just meant the capacity was higher and nothing else. However, my FAT16/32 library does not seem to be compatible.
By skimask
Put simply (and not entirely specifically correct, but should get the point across)...
SD cards address sectors by ignoring the lower 9 bits of the address. 4GB limit is due to 64bit limit on address.
SD-HC cards address sectors by using all of the bits in the address to point to an actual sector. The 32GB limit set on SD-HC is purely artificial. SD-HC cards, according to the spec should be able to address up to 2TB, but they reserve that for SD-XC.
By UhClem
Besides the change from byte to block addressing the card initialization is different. In particular ACMD41 must have the HCS bit set to inform the card that you can support high capacity devices. Otherwise initialization will fail.