There are two types of "rescue type" restore procedures involving optical media:
1. Everything OS on optical media.....you boot machine up w/ disk in drive and it does it's thing. If you have changed boot order, then have to go back into BIOS and put optical drive 1st in boot priority.
2. Most everything is on a hidden HD partition....put in optical media and it pulls the stuff off the hidden location. In this case, ya don't wanna format the hidden partition.