Answer： Because the bottom layer of the computer uses binary 1MB=1024KB. However, storage manufacturers use the decimal system for convenience when making U disks, hard disks and other storage devices. So this difference is caused. From GB to MB to KB to B to b. A total of 4 conversions are required. That is 1000/1024, which is 90.9%. In addition, the U disk itself needs to make room for storing its own information and as a spare area, so the actual capacity of the U disk is smaller than the nominal capacity of the U disk.