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I have a disk image file (iso) which is about 2.5GB, but when I mount and extract it, 13GB of files comes out. It means that it strongly compressed. I have UltraIso 9.5 but, it can not compress it as is was. It can just make compressed images in (isz) format which is not a standard one. How can I make compressed mountable iso images?

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There is no standard format (on Windows) for compressed image files (that I know of). There's PowerISO's DAA and MagicISO's UIF, but they both use zlib for compression, the same as ISZ, so I doubt the sizes would be much different. (I guess the files and not the ISO were compressed originally.) –  user55325 Dec 22 '12 at 7:55
    
The sizes are as I say, 2,5 --> 13. I can attach some screenshots. –  Hussein Pourakbar Dec 22 '12 at 8:05
    
the UDF format supports sparse files, so you could fit a 1TB file full of zeroes in a 20kB image. This is maybe what you are seeing. –  BatchyX Dec 22 '12 at 9:57
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