614 Chapter 21
was not released until it incorporated safeguards that prevented serial copying. This so
hindered the acceptance of DAT that it never became widely used, certainly not in Europe.
In contrast, the writeable CD was developed as a computer peripheral, and the record
industry did not realize what was happening until it was too late to stop it. Compared to
DAT, CD recording is fast, inexpensive, and easy, with no hindrance to making copies.
Copyright protection has, however, been developed for DVD (see 21.9 DVD).
To understand how the change in technology has come about, think back to how the early
CDs were manufactured, and are still manufactured. The CDs that you buy are made by
burning indentations with a powerful laser into the track surfaces of a master disc, using
the presence or absence of a pit to indicate a 1 or 0 digital bit. The player also uses a
laser, operating at a much lower power level and aimed at the track. The amount of light
that is refl ected from the laser beam depends on whether the beam hits a pit or an unpitted
piece of track. As the disc spins, these changes in intensity are detected and converted
into electrical signals, duplicating perfectly the digital signals that were used to create the
original. The advantage of this system is that it permits record pressing analogous to the
old vinyl disc method. The CD that is burned by the recording laser is used as a master to
make copies that can be used for stamping out plastic discs with the information intact.
This process, incidentally, is much less expensive than the method of recording tapes,
which need to be recorded from one end to the other, albeit at a faster speed than they are
played. It follows then that a CD is much less expensive to produce than a tape, and some
bargain CDs, even in the United Kingdom, are sold at prices that refl ect the lower cost.
The majority of issues, however, maintain the “ CD premium ” in prices, in the belief that
buyers will pay more for them even if they have cost less to make. You may have noticed
the low prices of magazines that have CDs attached, pointing out the low price that the
magazine has paid for the CD.
The more modern CD-R drives are recorded using a low-power laser that does not burn
pits into the plastic of the disc. Instead, the discs are coated with a dye that is affected
by the intense light from the laser. The effect is to change the dye color and, although
the change is not a vast one, it can be seen by the eye. If you look at a partly recorded
CD-R disc, you can see that the recorded portion (the inner part) is a quite distinctly
lighter shade of blue (usually) than the outer unrecorded portion. Because this change
is irreversible, the disc tracks can be written only once. This type of process is called
dye sublimation , and the surface appearance of the disc is also due to a thin metallic