Most DVDs are formatted to the ISO 9660 standard, which is portable. So, DVDs can be mounted by volume management.
To accommodate possible different formats, a DVD is split into slices. Slices are similar in effect to partitions on hard disks. The 9660 portion is portable. If you are having trouble mounting a DVD, particularly if it is an installation DVD, make sure that its file system is appropriate for your system's architecture. For example, you can check the label on DVD.