Associated constant in the API stacks: CDROM_SUPPORT. (Not reported in the USB descriptors.)
Suggested default: "Hard drive mode" (also known as "direct block access")
This checkbox causes the MSC interface to present itself as a CD-ROM, instead of a magnetic-media device. Generally speaking, any device not intending to appear as a CD-ROM should select "hard drive mode".
This box changes some fields the MSC interface reports to the host, and it causes it to use a different SCSI command set.
If using CD-ROM mode, you can only have a single logical unit (LUN).
What makes this mode useful is that cross-platform autorun functionality can be implemented with it. See USB example #M5 in the USB Developers Package, and its description in the Examples Guide.