CD-Rewritable
technology is one of the most recent optical storage
process. Using this special CD-RW media, you can
record and re-record a disc many hundreds of times
over. Each time, with perfect CD quality that’s
identical to the original source. And with all the
other advantages you expect from the CD format. But
with the big benefit of an effectively unlimited
writable and rewritable capability.
CD-RW technology
In its original state,
the recording layer of the CD-RW disc is
polycrystalline. During recording, a laser
selectively heats areas of the recording track above
the layer’s melting point (500 – 700 °C). The
melted crystals along the track flow into the
amorphous phase which is then ‘frozen-in’ by
quickly cooling the layer.
The
reflectivity of the amorphous areas is much
lower than that of the crystalline areas which
gives rise to the peak-and-trough pattern
along the recording track (just as the lands
and pits produce the pattern on a regular CD).
During
rewrite, some amorphous areas along the track are
returned to the crystalline phase by an annealing
process (heating at a temperature below the
layer’s melting point for a somewhat longer
period). Others are converted to the amorphous phase
by heating above the melting point This process can
be repeated more than a thousand times or even
higher.
The
recording tracks are read in the same way as
regular CD tracks: by detecting transitions
between low and high reflectance and measuring
the length of the period between the
transitions. The crucial difference is that
the reflectance is lower than for regular CDs
which means that the disc can not be read by
all CD mechanisms.
