In File Properties, What is Size and Size on Disk in Windows

December 29, 2011 at 20:05:25
Specs: Windows XP, All
What is meant by "size" and "size on disk" in windows?

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December 29, 2011 at 20:47:51
I bit more context might help a bit but I suspect you are referring to file size.

A file of a particular size might uses more space than it needs. A file that is 6kBs might uses 8 kBs of disk space

So the size is 6kBs and the size on disk is 8kBs

The difference is down to something called slack space. Slack space comes about due the the blocks that the hard dsik is divided up in known as clusters. With the NTFS file system the cluster size is 4kBs. So a file will always use multiples of 4 kBs on the disk. The bit left over at the end is slack space.

The biger the cluster size the more slack space which is essentially wasted space. With the Fat32 file system the cluster size can be as large a 64 kBs.. So a 4kBs file will use 64kbs of disk space. a 65kB file will use 128 kBs of disk space.



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December 29, 2011 at 21:11:49
My thoughts are.......
In Windows XPs NTFS file system, one Sector on the harddrive
amounts to 4,000 bytes. If a file is 1,000 bytes in size,
then that file will take up a full Sector, and you will lose

If a file is 40,001 bytes in size, the it will use 11 Sectors,
and you will lose 3,999 bytes of space.

Right click on a file,
then click Properties,
then look on the General tab,
you will see two pieces of information, "File size", and "Size on Disk".
"File Size" might be 100 bytes, and yet
"Size on Disk" would be 4,000 bytes.

I find LOG files in Windows that show
0 bytes of File Size,
4,000 bytes of Size on Disk.

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December 29, 2011 at 21:37:21
Slight correction, 1 KB = 1024 bytes, therefore 4 KB = 4096 bytes, not 4000 bytes

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Related Solutions

December 30, 2011 at 04:15:47
Files are made of clusters and clusters made of sectors. Most common is a 512 byte sector.

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December 30, 2011 at 04:40:12
Just a small addition; if the disk is compressed the size on disk might actually be smaller than the file size.

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