Use legacy emulation mode to work around direct communication problems between a guest operating system and a DVD or CD-ROM drive.
In legacy emulation mode, you can read only from data discs in the DVD or CD-ROM drive. Legacy emulation mode does not provide the other capabilities of normal mode. In normal mode, the guest operating system communicates directly with the CD-ROM or DVD drive. This direct communication enables you to read multisession CDs, perform digital audio extraction, view videos, and use CD and DVD writers to burn discs.
If you run more than one virtual machine at a time, and if their CD-ROM drives are in legacy emulation mode, you must start the virtual machines with their CD-ROM drives disconnected. By disconnecting the CD-ROM drives in the virtual machines, you prevent multiple virtual machines from being connected to the CD-ROM drive at the same time.