I'm sure an engineer could be more precise on how SD works. As I understand it, the SD card contains an identifier, like a credit card number, embedded in it. When downloading music, the source looks for the identifier and then automatically signals that the user should be billed. If the user then tries to make a copy of the music or other file, the SD card looks for a similar identifier, and if that identifier is not found, then it won't permit a copy to be made. Thus, there is a built-in control that prevents unauthorized copying to unknown devices. Of course, if you played the music selection through a reasonably good amplifier, you could tap the audio (analog) signal and make a recording, but the quality wouldn't be as good as the original digital copy.
In an application such as Napster, where files are uploaded to a storage facility and then downloaded by someone else, a secure digital card would allow such copying if the artist waived the right to receive any fee. Or, the artist could demand a nominal fee, which could be charged to the indentifying code on the SD card. |
