Overburn is a process of burning more that 74min on a 74min cdr. It depends on a few things, the burner, the software and the cdr you are using. Now, Nero supports overburn and even has setting in the preferences to set the limts Nero will work with. In order for it to work, your burner needs to support it. I think the
Nero site has a list of burners that do and don't support the over burn. What makes the burner support it is how far the laser can travel on the rails that support it. The last thing you need is the cdr media. Once again, I think the nero app can examine your media and tell you how far it will overburn.
Why to overburn? several reasons. YOu can fit more data on a cdr, so you get more bang for your buck! Another reason is backing up ssoftware. One way that has been used to keep people from copying software is to make CDs with more that 650megs of data on it. If you can overburn, you can back up this software
Brands that I knwo overburn:
Yamaha
Teac
Other bardns do it, but I just son't knwo if "all" models by those manufacturers do it.