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Why is the effective hard drive size lower than the actual size?

This might be a duplicate, but my current search can't find the answer.

I've created a simple partition, 50 MB, NTFS on a Windows 7 install.

I have about 2000 files, total space used by the files is 27 MB. But yet the disk shows on 2 MB free.

I've checked the following hidden users of disk space

  • Recycle bin
  • Shadow copies
  • Paging files
  • Plain vanilla hidden files via WinStatDir

None of the above are being used.

Where are the missing 21 MB of space?

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marked as duplicate by Oliver Salzburg Dec 19 '12 at 12:26

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

A 50MB partition? Are you sure you haven't lost a few zeroes or did you mean GB? – Nifle Oct 12 '10 at 22:00
50MB :) there's a reason. Really. The drives are shared and need to be visible to DOS programs via XP Mode. – Scott Weinstein Oct 12 '10 at 22:07
up vote 5 down vote accepted

One freshly created 50 MB drive NTFS will take arround 35 MB for it's internal structures. This is something that you lose before putting ANY file on it.

NTFS is just not suitable for small drives. I would recommend that you format drive with FAT. It has much less overhead and there is no real benefit on such a small drive from NTFS anyhow.

Of course, if you need NTFS security, only solution is to make bigger drive.

P.S. Here is what things look like on EMPTY 50 MB NTFS drive:

48127 KB total disk space.
 5184 KB in 6 files.
   12 KB in 13 indexes.
    0 KB in bad sectors.
 2723 KB in use by the system.
 2048 KB occupied by the log file.
40208 KB available on disk.

on 50 MB FAT drive there is almost no overhead and you will have 47920 KB available.

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I posted an explanation to an earlier question as to why you cannot simply add up the total space and expect that to match up to the amount of free space.

I think it applies to this too. NTFS doesn't have the deleted files but still existing, but the other two points still apply.

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but 21 MB of space due to slack? – Scott Weinstein Oct 12 '10 at 23:00
Not just slack, like Josip says above, the filesystem overhead is in play here too. – gorilla Oct 13 '10 at 0:00

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