Megabyte vs mebibyte: why your drive looks smaller
Buy a 1-terabyte drive, plug it in, and your computer reports about 931 gigabytes. Nothing is broken — two different counting systems are colliding.
Drive makers count in decimal: one kilobyte is 1,000 bytes, one megabyte is 1,000,000 bytes. Operating systems historically counted in binary: one kibibyte is 1,024 bytes, one mebibyte is 1,048,576 bytes.
The gap grows with size. At gigabytes it is about 7 percent; at terabytes it is about 9 percent. That is the missing space on every drive you have ever bought.
The binary units have official names — kibibyte, mebibyte, gibibyte — precisely to end the confusion. If a size is labelled MB, check whether the maker means 1,000,000 or 1,048,576 bytes. A converter that offers both will tell you in one click.