Different byte size and item count for same data on internal/external drive

Discussion in 'iMac' started by ggulliver, Sep 6, 2012.

  1. ggulliver macrumors member

    Jan 22, 2008
    I'm wondering why there's a difference in the byte size and item count when an assortment of data stored on my internal drive is replicated on an external drive.

    Although sometimes the byte size and item count is identical, it's usually lower on the external drive.

    Here's an example, with three folders of mixed mp3, avi txt files. The first figures are for internal drive, the latter for the same items on the external drive. :

    Folder 1: 35,041,200,905 bytes (35.04GB on disk) for 121 items; 35,041,194,761 bytes (35.04GB on disk) for 121 items.

    Folder 2: 45,821,885,162 bytes (45.82GB on disk) for 732 items; 45,821,885,162 bytes (45.82GB on disk) for 726 items;

    Folder 3: 461,292,486,016 bytes (461.45GB on disk) for 82,889 items; 461,292, 486,016 bytes (461.45GB on disk) for 82,795 items.
  2. Puevlo macrumors 6502a

    Oct 21, 2011
  3. charlieegan3 macrumors 68020


    Feb 16, 2012
  4. ghellquist macrumors regular

    Aug 21, 2011
    Stockholm Sweden
    Item count: due to hidden files.

    There is a way to change a flag and then show hidden files in the normal window, but it fast gets annoying.

    Instead start terminal and go to library by the command cd. Then do ls -a to see all files.

    Hidden files normally has a name starting with a . and are normally not copied (except by backup programs).

    You could also get quite different size on discs for the same set of files if the block sizes happen to differ. This does not seem to be the case for you. Each file always takes a full block, even if it only happens to fill a small part of it. So, if an example, block size is 4096 a small file of 100 bytes will take 4096 bytes on that disc. On a different disc, block size might be 1024 bytes and then the file will only need one block at 1024 bytes. Caveat: this is nothing a normal user needs to even think about, that is the job of the operating system.

    // Gunnar
  5. ggulliver thread starter macrumors member

    Jan 22, 2008
    Thanks for the answers - and sorry for my delay in returning.

    I wondered about hidden files - thinking that they may not have been copied.

    I decided to not use the terminal to show hidden files - last time I did this it littered my machine with all sorts of stuff... and even with them showing, it'd be impractical to check all folders to see the differences and which of the copied folders had such files that hadn't been copied.

    I decided instead to 'trust the process' and not be so anally curious about stuff that I probably shouldn't bother with.

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