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Windows 7: C: Drive Used/Free Space WAY Different Than Actual?

02 Sep 2014   #11

Windows 7 Pro 64 bit

Slack space is one of many factors that complicates disk space usage calculations. Each file is made up of a number of allocation units known as clusters. Typically they will be 4096 bytes. If a file consumes exactly 1 cluster adding 1 more byte will require the allocation of another cluster just to store that one byte. The rest of the cluster will be wasted. A factor that partially offsets this waste is that very small files may be stored entirely in the MFT (if the drive is NTFS formatted) and not require any extra clusters for it data. How large such a file can be depends on the storage requirements of the other attributes of the file, such security settings. If the file simply inherits it's security settings from the parent folder this will not be much. But if it has settings of it's own it could require substantial space. Then there is the fact that folders are themselves files which consume disk space.

And there is more. Much more.

Windows Explorer and other utilities ignore most of these factors or makes arbitrary decisions. In many cases how much these factors would effect the calculations is unknowable.

My System SpecsSystem Spec

 C: Drive Used/Free Space WAY Different Than Actual?

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