Why does my hard drive report less capacity than indicated on the drive’s label?

Explains why a hard drive's capacity often appears to be less than advertised when showing in (My) Computer or Mac Disk Utility. Hard drive manufacturers market drives in terms of decimal (base 10) capacity. In decimal notation, one megabyte (MB) is equal to 1,000,000 bytes, one gigabyte (GB) is equal to 1,000,000,000 bytes, and one terabyte (TB) is equal to 1,000,000,000,000 bytes. Programs such as FDISK, system BIOS, Windows, and MacOS use the binary (