SCMS stands for "Serial Copy Management System" and is the way copies of digital music are regulated in the consumer market. It is information that is added to the stream of data that contains the music when one makes a digital copy (a "clone"). When making an analog copy only the music is transferred so there is no SCMS, and copying is totally unrestricted. Decks considered "professional" -- usually more expensive and with pro features, such as balanced XLR input/output -- are exempt from needing SCMS. Different manufacturers' pro decks behave differently: some allow one to set the SCMS code how one wishes, some only if the pro i/o is used, and some ignore it completely.

SCMS Bit Definitions

SCMS Operation on consumer decks

Dubbing MD to MD with SCMS

SCMS does not limit the number of times you can copy a certain CD or MD. For instance, you can make 20 copies of a CD - you just can't copy any of the 20 copies.

It is ironic that if SCMS is to prevent unauthorized duplication of copyrighted information it has the above loopholes that a professional ripoff artist can easily use. And it is unfortunate that supposedly legitimate users, such as musicians recording their own music on cheaper, consumer decks, are restricted in the number of generations they can copy their music.