I have a Philips Audio CD recorder.  It's drive can
handle both CDR's and CDRW's.  There is, in fact, a header on
each type of disk that identifies it as either a CDR, CDRW, or
just plain CD.  The header can also identify a RIAA CDR or CDRW
which is, in fact, exactly the same as a non-RIAA CDR or CDRW
except that the header says that the disk has been blessed by the
Recording Industry of America and a special tax has been paid
because they know you are going to use the disk to steal.

        The real difference between a lot of CDR's and CDRW's is
the surface reflectivity at the IR frequency that actually counts
in the recording/playback cycle.  The laser in a CDRW drive tests
several levels of power before deciding on the optimum power.

        When you have finished burning a CDRW, it may play just
fine in other CDRW drives, but not in a CDROM-only drive unless
it was specifically made to play CDRW's.  That is the real catch.
The CDRW's don't reflect enough IR back to the pickup.

        I have, in fact, run across some CDR's that didn't
reflect enough light, either, so you had better try your disks
where they will be used to make sure they will work.

        Someone mentioned the inability to add more stuff to some
CDROM's.  That is right, but it is more to do with software than
hardware.

        Audio CD's have a different file structure on them than
computer CD's.  The table of contents is started on one part of
the disk and kept there until the disk is "finalized."  At that
point, a new directory is created in a different location and the
original directory is copied to that point.  Don't ask me why
because I don't know that.

        After the disk is finalized, you can't add anything to
it.  If it is A CDRW, you still can't add to it unless you erase
the entire disk and then it is like new again.

        I am not sure how or if the finalization process applies
to CDR's and CDRW's with data file structures on them.

        Again, the biggest headache right now is to be sure your
finished archives can be read on the drive that will be using
them because of the different reflectivity coefficients of the
different CDR and CDRW media.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Data Communications Group

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