For Nero Burning ROM, the template for creating a bootable disc can be either a logical drive or a drive image file which contains the contents of a drive as a file sector for sector. If the template for the bootable disc is a logical drive, the bootable disc will emulate this when the system is booting. There are three emulation types: 
 
 
 
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Floppy emulation: This requires a bootable floppy disc for creating the bootable disc. At startup the bootable disc emulates a floppy disk. In the process, the drive letters increment, so that Drive A: corresponds to the bootable disc. The volume of the start data is limited by the capacity of the floppy disk (e.g. 1 MB).
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Hard drive emulation: A bootable hard drive is required to create the bootable disc. At startup the disc emulates Drive C. All drive letters from Drive C increment by one. The volume of the start data is limited by the capacity of the CD (e.g. 700 MB) or DVD (e.g. 8.5 GB). If, for instance, you have a 200 GB hard drive with only one (200 GB) partition, you cannot create a bootable disc from it without repartitioning your hard drive accordingly beforehand.
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No emulation: In this process the drive names are not changed. This type is used for bootable installation CDs. This setting is intended for users who do not require a floppy or hard drive emulation and who want to install their own device driver.

Bootable Disc Template