How do ISO files work?

[johnny44]

Just a quick question someone might be able to answer. I built 8 different XP installations that total 3.3GB. When I burn the ISO, it is 1.3GB. Everything works perfectly. Why is the ISO file so much smaller? Are the duplicated files overwritten? Does it only add pointer to duplicated files?

Thanks

[CptMurphy]

The file is proabably optomized. Also, an ISO is a type of compression but again, you mainly see this when the iso is optomized.

[johnny44]

Thanks m3n70r. I think Powerpacker uses cdimage.exe to create the ISO file. It probably uses the -oc or -oi switches which are used to optimize. I guess the big difference makes sense to me now since most of the files are duplicates.

The only remaining question is, if it skips duplicate files what does it put instead? A pointer to the location of the file it kept?

[LLXX]

The only remaining question is, if it skips duplicate files what does it put instead? A pointer to the location of the file it kept?

Correct.

See http://en.wikipedia.org/wiki/ISO_9660 and http://en.wikipedia.org/wiki/ISO_image for more info.

Edited February 15, 2006 by LLXX