Why your 1 TB hard drive always shows 931 GB, explained

When you plug in a 1 TB hard drive, your operating system typically reports only 931 GB — a gap rooted in two conflicting definitions of a gigabyte. Drive manufacturers count a gigabyte as exactly one billion bytes (base 10), while Windows calculates it as 1,073,741,824 bytes (base 2), creating a roughly 9.95% discrepancy at the terabyte scale. A 2004 lawsuit, Safier v. Western Digital, challenged this practice but failed because both the drive maker and the OS were technically correct under their own definitions. In 1998, the International Electrotechnical Commission proposed distinct binary prefixes — such as GiB and TiB — to eliminate the confusion, but the standard has seen little adoption over the past 27 years. The ambiguity persists partly because each stakeholder — manufacturers, software vendors, and OS developers — has little incentive to abandon the familiar terminology.