That’s the good news, and for some users this is the perfect technology —
a huge, fast equivalent to the original floppy disk. The bad news, though, is
that CD-RWs are more expensive than CD-Rs and are sometimes more per-
snickety about moving from one machine to another.The trick behind CD-RW is the use of some more expensive inorganic or
metallic compounds — often an alloy of silver with exotic elements like
indium, antimony, and tellurium. And then there is a hyper-powered tiny
laser, capable of heating pinpoints to 500–700° Celsius, about 900–1,300°
Fahrenheit.The high heat actually melts the crystals, changing them to a noncrystalline
structure; when the laser reads back the information, these areas reflect back
less light than the surrounding crystal. To erase a CD-RW, the laser shifts to
a midway power of about 200° Celsius, enough to change the alloy back to a
reflective crystal form.A CD-RW should be capable of being recorded to, erased, and rerecorded
dozens or even hundreds of times. However, just as with a floppy disk, don’t
plan on using a CD-RW over and over again as the only repository of irre-
placeable data. You would be better off using a CD-R just once and placing
that archive in a safe or other protected place.How Fast Is Fast and How Big Is Big?.........................................................
Although CDs, CD-Rs, and CD-RWs are very similar in design, especially when
it comes to reading data recorded on them, they can and do vary in their
specifications. All CDs store information in grooves that are 1.6 micron wide.
A micronis^1 ⁄1,000of a millimeter; 1 inch is a bit more than 25,000 micros in150 Part III: Laying Hands on the Major Parts
Price and prejudice
CD-Rs are very inexpensive; as this book goes
to press you can buy a spindle of 100 discs for
the equivalent of about 25 to 40 cents apiece; if
you must have a separate jewel boxfor each
disc, the price increases to about 60 to 75 cents
each. At one time CD-RWs cost as much as $5
apiece, but the price differential has greatly
improved in recent years; today you can buy a
spindle of 100 CD-RW discs for the equivalent of
about 60 to 75 cents each, or about $1.00 in ajewel case. Many compatibility issues have
been solved, but you cannot be 100 percent
sure that a CD-RW made on your laptop is going
to work in a CD-R on your desk or a CD player in
your car. Run some tests to find out for yourself.
In my office, I’ve decided that the less expen-
sive and more broadly compatible CD-R is the
way to go; I buy them in 100- or 250-disc spin-
dles and give no thought to making backup
copies whenever and wherever.