I recently purchased an external Hard Drive with 1TB if storage capacity.
The only problem here is when I'm in Windows 7, it shows that it has 930GB available but on Ubuntu it's 993GB. The HDD is partitioned as NTFS.
Which one says the truth?
Unfortunately, Windows always calculate hard drives as powers of 1024 while hard drive manufacturers use powers of 1000. On other hand Ubuntu uses the Standard 1000 division.
Most manufacturers of hard disk drives define,
While Ubuntu and Windows see it as:
Ubuntu is showing capacity as 993 GB, because that missing space might be used up by the allocation table and other meta data.
This wiki article explains the issue :
This SU answer is a very good Explanation on Storage Size Calculation.