Contents of the SCMS.TXT file
The Serial Copy Management System (SCMS): How It Works
As its name implies, the Serial Copy Management System (SCMS) is a
technical method for controlling "serial" digital copying on Digital
Audio Tape recorders (DAT). The term "serial" copying denotes the
copying of copies, i.e., the making of a second, third and successive
generations of tapes from a first (or subsequent) generation copy.
SCMS will allow any original prerecorded work, as well as other
material, to be copied indefinitely onto different blank DAT tapes.
However, it limits the number of digital-to-digital copies that can be
made from the copies, unless the source material is both digital and
How does the system operate? The circuitry which controls the
functions of the DAT machine will be programmed to read certain coding
information contained in the digital subcode channel. Based on the
particular combination of codes it reads, the circuitry will either
permit unrestricted copying, permit copying but label the copy with
codes to restrict further copying, or disallow copying. DAT recorders
are generally equipped with both a digital input and a pair of stereo
analog line inputs. Before a DAT machine records, the machine will
first determine whether the music to be recorded is entering via the
digital inputs or the analog inputs of the recorder. Once that
determination has been made, SCMS will implement one of several forms of
copy prevention or limitation, depending on the source, the input, and
whether the music is marked for copyright protection.
-- Recording through Digital Inputs --
If the source material is marked for copyright protection and enters
through the digital inputs, the DAT recorder will produce one or more
first-generation copies of the original prerecorded music, but further
digital-to-digital copies cannot be made from the first-generation
copy. Copies of digital broadcasts will be treated in the same way.
All digital recordings and broadcasts have digital subcode channels
which contain important coding information. These channels are located
apart from the channels that carry the music. One of the pieces of
information contained in the subcode channel is the "category code,"
which tells the DAT machine what type of digital device is being used as
a source (e.g., a compact disc player, whose output is protected, or a
digital microphone -- a mike with an internal A/D converter -- whose
output is not). Whether or not the material is marked for copyright
protection is signified by a "copyright flag", also carried through the
digital subcode channel. The machine uses the combination of category
code and copyright flag to determine whether copying is permitted. If
it is, the recorder ensures that the blank DAT tape will carry the
appropriate copy protection codes by writing them into the digital
subcode channel of the new tape as it is being recorded.
If the category code indicates an identifiable digital source and the
material being copied is marked for copyright protection, or if the
digital source cannot be identified, an identification code" of "1,0" is
written onto the digital taped copy as it is being recorded. It is this
code that prevents further direct digital copying from the copy. Thus,
if the machine detects an identification code of "1,0" because a first
generation copy is sought to be digitally copied again, the DAT record
function will not operate.
If the material is being copied from an identifiable digital source
and is not copyright protected (e.g. a digital microphone), the recorder
will mark "0,0" in the digital subcode channel. This code will not
limit future serial copying.
These identification codes are located exclusively in the non-music
channels, so they cannot effect the sound quality of the recording in
-- Recording Through Analog Inputs --
The SCMS system also places restrictions upon the number of
generational copies that can be made of music entering via the analog
inputs of a DAT recorder. A DAT recorder is unable to determine whether
this material is copyrighted or not, since current technology does not
permit such identification in the analog domain.
Accordingly, any material recorded via the analog inputs would cause
the DAT to mark a copy protection identification code "1,1" in the
digital subcode channel of the DAT tape. This subcode marking would
indicate that one more digital-to-digital copy could be made from this
first-generation copy. When this first-generation copy is digitally
copied again, the second-generation copy would be labelled with the
"1,0" identification code, thereby barring subsequent digital copying of
-- Summary --
o SCMS does not require any action on the part of the
listener. There are no additional buttons or controls
to complicate the recording process.
o Copying of digital copyright protected material is
limited to copying from the original. Subsequent
digital copies cannot be made from the copies.
o SCMS does not affect copying on a conventional analog
o Copying from conventional cassettes, LPs or radio
broadcasts to DAT will allow recording of the first DAT
tape and one digital-to-digital generation of copies from
that tape. After the second generation, further
digital-to-digital copying from the copy is prohibited.
o The codes that are written onto the blank DAT are not
audible because they are located in the digital subcode
This information is provided by the Home Recording Rights Coalition.
For further information, or to receive future press releases on the
subject of home recording, write or call:
Home Recording Rights Coalition
PO Box 33576
1145 19th Street NW
Washington, DC 20033