iso is a standard,it's like was said already an exact copy of the disc all in one big file..with everything in it's proper place...most standalone burner progs like nero will handle it fine. for most cd's copying either way will give you a useable back up..iso comes in handy for cd's that are a bit more complicated...for instance bootable cd's like winXP/win2k etc. a straight file copy of these cd's will work fine from within windows but it won't be much good if you have no OS or need to get into the repair console...you can't see everything that is on the disc to copy it,to get the boot sector you need a bit for bit copy,ISO gives you that. there are other advantages in certain situations as well,if you need to keep a copy of a cd on your hardrive for later burning then it's all in one big file...or if you need to burn multiple copies of the same cd you have a single "source file" and don't have to keep selecting/copying the original cd/files everytime you need to make a copy...it's also been known to get around some types of weaker copy protection and generate a useable disc where a straight file copy fails to get whatever is hidden on the disc. for most stuff a straight file copy is fine...but i always use an image file like an iso..if you're gonna make a copy..why not make an exact copy?it's usually just as easy and sometimes quicker