They allow the user to run computer software without having to insert their required CD-ROM or DVD-ROM.
No-CD cracks specific to a variety of games and other software distributed on CD-ROM or DVD-ROM can be found on the Internet from various reverse engineering websites or file sharing networks.
No-CD cracks have legal uses, such as creating backups of legally owned software (a user right by law in many countries) or avoiding the inconvenience of placing a CD or DVD-ROM in the drive every time the software is being used, although they can also be used to circumvent laws in many countries by allowing the execution of full versions of non-legally owned applications or time-limited trials of the applications without the original disc.
Some programs, however, attempt to discover such disk image emulators and will refuse to work if one is found.
Other programs exist that attempt to hide the presence of disk image emulators from such protected software.