Why are some disk images bigger when burned? I've got a couple of DMGs that should fit on a CD (one per CD) but burning softwares (Disk Utility &amp; Toast) say that they are 2 or 3 times bigger and thus need a DVD.
Why is that ?
Different file systems and disk formats have different block sizes, which all files are rounded up to in size.  If you have a lot of small files on one file system, and try to move them all to a different file system or media format with much larger block sizes, the total space required can balloon.