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Different Folder Sizes Shown in Properties

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  • Different Folder Sizes Shown in Properties

    When I on a Folder's Properties I get 2 sizes shown . For instance , if I on Properties on the C:\Windows\System32 Folder , I get the following :-

    Size:- 1.02 GB

    Size on Disk:-874 MB

    Why the difference?

  • #2
    Re: Different Folder Sizes Shown in Properties

    All file systems allocate space on the HD via a method of pre-defined clusters, which can be of varying sizes. Unfortunately not every file is written up so that it is exactly a multiple of your cluster size, but in order to keep things flowing smoothly, your File system 'allocates' the next largest integral multiple of clusters that is will hold your program or file.

    To make it a bit more simple, think of this:

    Your HD has X amount of space, and your File system (NTFS for XP/Vista) uses 4K clusters - in other words, each allocation unit is 4K large. Now, anything less than 4K in size will still take up 4K of space on the HD, as the file was pre-allocated that much space because of the file system In actually, the file may only be 2.2K in size, but on the HD it is still allocated 4K, and that 4K is not able to be used by anything else (so as to prevent confusion to the File system).

    Now, if all your files were multiples of 4K, then the size and size on HD would be the same - however, because of the above example, almost every file has more space allocated than it actually uses - this is called slack space - and the larger the drive, or the more files you have, usually the larger the slack space you have as well.

    For some further reading, see these:


    • #3

      Thank for the reply.

      I'd forgotten about cluster size - thanks for the refresher.



      • #4
        Re: Different Folder Sizes Shown in Properties

        Another issue you should not forget is the compression on an NTFS partition/volume with compression enabled. It will also influence the size on disk that a certain file will get.

        Sorin Solomon

        In order to succeed, your desire for success should be greater than your fear of failure.