http
/www.techimo.com/forum/storage-related/157623-real-advertised-hard-drive-sizes-why-you-dont-get-all-space-you-pay.html
In short, the manufacturers count Gigabytes as 1,000,000,000 bytes but in reality a Gigabyte is 1,048,576 Bytes. So that drive being advertised as 500GB correct being 447GB. It's stupid I know but blame the manufacturers.