It hold the amount of storage that's "advertised", but you have to read the fine print.
All storage devices -- Flash drives, HDDs, SSDs, & probably even DVD-Rs & CD-Rs -- use the "1 TB = 1,000 GB = 1,000,000 MB = 1,000,000,000 kB = 1,000,000,000,000 bytes" when listing their storage size. It's basically the metric system for storage.
All operating systems -- Windows, Linux, Mac OS X, Android, iOS, etc. -- use the "1 TB = 1,024 GB = 1,048,576 MB = 1,073,741,824 kB = 1,099,511,627,776 bytes". That's because it's based on the binary system, & 2^10 = 1,024.
So, a drive advertised as holding 1 TB of data means that it holds 1 x 10^12 bytes of data...which, to the OS, will appear as 931.32GB (or...