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I have an external Lacie hard drive connected via USB to my Macbook Pro which is running Snow Leopard. I have nothing but music on the external drive with every album sorted in it's own individual folder and have changed all of the individual folder icons to display the album art of the songs from the album inside. I want to reformat my laptop, but I'm afraid if I do that, the album art will disappear if it's stored on a system file within the main hard drive OS. My question is this, is the information which tells the OS to display the album art listed in a hidden system file on the external Lacie drive or my laptop hard drive and if I reformat will I have to reassociate all of the album art to the folders on the external or will it keep it's associations. Thanks in advance.

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If you change the icon for a folder this way, the icon information is stored as an invisible file called .VolumeIcon.icns inside the folder. This means the custom icons on your external drive will also be displayed if you connect it to another mac (or your own reformatted mac).

I don't know if you can make OSX display custom icons in other ways (ie, some system specific setting). If you want to check whether the .icns files are actually in your folders, check out the hiddenfiles Widget, which lets you toggle visibility for hidden files.

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.icns files are used for Volumes icons.

Inside each folder you can find an invisible file called Icon? (the ? is actually the character 0x0D), which should contains the custom icon.

I tried removing this file and the custom icon vanishes, however the size of this icon file is 0.
So I don't know if it really holds the icon.

I tried to copy it to another folder, but the new folder doesn't get the custom icon.

If you have another computer running Mac OS X or a friend having a Mac too, try plugging the disk in its computer to check if on another computer the custom icons are still here.

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The custom icon data for folders is the in resource fork of the "Icon\r" files (ls -l folder/"$(printf 'Icon\r')"/..namedfork/rsrc). But it there is also a special flag that controls whether it is used. If you move the "Icon\r" file from one folder to another you have to also set the “custom icon” flag for the destination folder: /Developer/Tools/SetFile -a C /path/to/folder See… – Chris Johnsen Feb 20 '10 at 3:18
@Chris is correct: The file appears to be empty because all the data for an Icon\r file is in the Mac OS Resource fork. – Josh Feb 25 '10 at 13:52

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