1, the memory manufacturer produces according to the algorithm of 1000m= 1g, and the file binary is always calculated according to the method of 1024m= 1g! So even the memory card in it is an empty disk of 16g, which can't display the actual whole 16g!

What's more, the intelligence of smart phones comes from software. The memory card is not an empty disk, and the system and software are all in it. They occupy at least 2-4g of space, so it is completely realistic that there is a certain error in capacity.