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I'm using fsutil to get info about a drive. Here's actual output:

NTFS Volume Serial Number :       ...
Version :                         3.1
Number Sectors :                  0x0000000004fccfff
Total Clusters :                  0x00000000009f99ff
Free Clusters  :                  0x00000000006d6faf
Total Reserved :                  0x00000000000017c0
Bytes Per Sector  :               512
Bytes Per Cluster :               4096
Bytes Per FileRecord Segment    : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length :           0x0000000003cc0000
Mft Start Lcn  :                  0x00000000000c0000
Mft2 Start Lcn :                  0x0000000000000002
Mft Zone Start :                  0x000000000030d7c0
Mft Zone End   :                  0x0000000000319fe0
RM Identifier:        ...

Shouldn't the (Number Sectors * Bytes per Sector) equal (Total Clusters * Bytes per Cluster)?

The sector-based calc: 83677183*512 = 42842717696

The cluster-based calc: 10459647*4096 = 42842714112

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up vote 1 down vote accepted

Divide Bytes Per Cluster by Bytes Per Sector and you will find that you have eight sectors per cluster. Now divide Number Sectors by eight and you will see that it is not evenly divisible (10459647.875 clusters). Drop the fraction (you can round down, but not up) and the total number of clusters is 10,459,647 (0x009F 99FF).

As a result, there are some sectors that are unused:

Total Sectors                            =        0x04FC CFFF
Total Clusters x Sectors Per Cluster (8) =   -    0x04FC CFF8
Bytes Per Sector                         =   x            512
Unnused/Wasted Bytes                     =              3,584 (3.5KB)

Your calculations:
Sector-based  calc (83,677,183 x  512)   =     42,842,717,696
Cluster-based calc (10,459,647 x 4096)   =   - 42,842,714,112
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awesome, thanks very much. +1 – jglouie Mar 9 '12 at 20:52

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