When you mount a Mac-formatted multisession CD or a dual-format CD, you can select view options for each from the disc shortcut menu.
Some CD-ROMs have both Windows (ISO-9660) and Mac (HFS or HFS+) volumes on them. You can choose which volume to access from the disc shortcut menu. The effect is much like ejecting one disc and inserting another. Mac HFS+ Disk Support remembers which volume, Windows or Mac, you last used on a particular disc, and will return you to that setting if that disc is used again.
A list of available volumes appears in the disc shortcut menus of multisession CD-Rs. Selecting a new volume causes the current volume to disappear, and the new volume to appear in its place. The effect is much like ejecting one disc and inserting another. Mac HFS+ Disk Support remembers which session you last used on a particular disc, and will return you to that session if that disc is used again.