6416 CD-RW - Part 5
Technology Part II
Over at the top, we have the power levels of the laser during
recording. There are 3 levels, Pwrite, Perase and Pbias. The CD-RW
drive has to be pulsed to form well-defined amorphous regions. This
is different from traditional CD-R drives where the laser is left at
constant power and the only thing change is the time required to
form the "pit" on the dye.
this write strategy writes new data to the disc and at the same
time, it simultaneously overwrites old data.
So, how does a CD-RW rewrites it's data? The CD-RW drive uses pulsed
beam to write amorphous "pits" as well as non-pulsed beam
to write crystalline "lands" between the "pits".
Hence this write strategy writes new data to the disc and at the
same time, it simultaneously overwrites old data. This procedure can
be repeated for several thousand times. Totally cool!
I will just give a
brief explanation on the various types of CD-R dyes used. There are
currently two popular dyes used in the market. The CYANINE
dye as well as the PHTHALOCYANINE (pronounced
CYANINE dye can be
identified by their emerald green or cobalt blue color. This is the
most popular dye you see in the market. The dye itself is blue, but
may appear in different colors based on the material used for the
reflective layer. For example, a gold reflective layer will produce
the green color while a silver reflective layer will produce the
PHTHALOCYANINE dye can
be identified by thier almost clear yellow-green color. You see them
in CD-R which appear gold or greenish gold. Lifetime of the
PHTHALOCYANINE are longer than CYANINE dye and estimated to be about