As dpilot83 is alluding to, the dvd has to be burned as a system disk to be recognized. In other words, it need a basic operating system burned directly to the disk so that the computer BIOS can hand over control. The BIOS doesn't know how to read file systems so just looks in a specific spot on the disk to load whatever is there. That file (bootMGR) takes control of the computer from that point and loads whatever o/s is on the disk.