Hi.
I not sure if this is the info you are looking for
http://alumnus.caltech.edu/~pje/iso9660.html
On the previous link you can found all the related information about the standard ISO format, you must know that the UMD ISO format is based on it, but with some diferents.
This info is needed if you want to look for a file or folder inside a iso file, about where is stored all the information related to LBA, position, size,etc.
Regards
Spirax