That's the normal size for a 1TB drive. What you're seeing is the difference between binary (240) and decimal counting (1012 ).
HD Manufacturers: 1000 Bits = 1 Byte and 1000 Bytes = 1MB and 1000 MB = 1GB and 1000GB = 1TB
1000 X 1000 X 1000 = 1,000,000,000,000 or 1TB
MB = 1GB
1,000,000,000,000 / 1024 / 1024 /1024 = 939.3225746154785
(I did that in my head, so it might be off in the last decimal place.) <= Big Fat Lie
The other ~.9 etc is the 100MB System Reserved space at the beginning of the drive. Terabyte - Wikipedia, the free encyclopedia