however Windows shows the capacity as 931GB with 914GB of free space. I know the actual capacity of a drive is usually less than the stated, but by nearly 69GB!
It is most likely because of the confusion when the computer world uses the standard k, M and G as something else than 1000 (computer k=1024), 1000000 as M=1048576 and so on.
In the computer world 1 GB is not 1 000 000 000, but 1073741824.
Windows says your drive is 931 GB. Take "computer G" 1073741824 * 931 and you end up with 999 653 638 144, which is very close to 1TB (real T). So it is not Windows that fools you, but somewhat Samsung that sells their drive which really is almost 1TB (i.e. 1000 000 000 000), but not computer-TB...
Do I need to format a drive for Windows 7?
No, it is being done by the Windows installation program.