Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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?

share|improve this question
Where do you see those capacities ? You might be confusing formatted space versus drive capacity. – BatchyX Dec 15 '12 at 19:16
This may be of assistance... – Breakthrough Dec 15 '12 at 19:16
@BatchyX I simply open up the properties window of the mounted drive. – Hamed Momeni Dec 15 '12 at 20:15
up vote 8 down vote accepted

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,

1 TB = 1000000000000 bytes = 10^12 bytes

While Ubuntu and Windows see it as:

1000000000000/1024*1024*1024 = 931 GB (Windows style) (should be gibibyte (GiB))

1000000000000/1000*1000*1000 = 1000 GB (Ubuntu style)

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 :

Microsoft Windows reports size in gigabytes by dividing the total capacity in bytes by 1073741824, while still reporting the result with the symbol "GB". This practice is a cause of confusion, as a hard disk with an advertised capacity of, for example, "400 GB" (meaning 400000000000bytes) might be reported by the operating system as only "372 GB". Other software, like Mac OS X 10.6 and some components of the Linux kernel measure using the decimal units.

This SU answer is a very good Explanation on Storage Size Calculation.

share|improve this answer
Thanks. I guess you're right. The math makes sense now. – Hamed Momeni Dec 15 '12 at 20:20
You are welcome. Glad, to be of help :) – Ankit Mishra Dec 15 '12 at 20:24

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.