Storage values must be positive
Decimal (SI — used by storage manufacturers)
Binary (IEC — used by operating systems)
Bits
Hard drive manufacturers use decimal prefixes (1 KB = 1,000 bytes), which produce larger-looking numbers. Operating systems use binary prefixes (1 KiB = 1,024 bytes), which is why a "500 GB" drive appears as roughly 465 GB in Windows or macOS. The IEC introduced the kibibyte, mebibyte, and gibibyte in 1998 to make this distinction unambiguous, though the old names are still widely misused.