Hardware Reference
In-Depth Information
CD and DVD Drive Interfaces
CD and DVD drives use the same connectors as hard disks do to the motherboard.
Depending on the model, they can use PATA, SATA, or SCSI, which were described earlier
in this chapter.
CD Writing Technologies
CD-ROMs are read-only, but there are two technologies for creating your own CDs: CD-R
and CD-RW.
CD-R
, which stands for
Compact Disc Recordable
, can be written to only once (except
in the case of multisession writing, where the previous content isn't exactly erased, but
ignored, and the new content shown in the disc's fi le listing instead).
CD-RW
or
Compact
Disc Rewriteable
can be written to, erased, and reused many times, functioning somewhat
like a fl ash RAM drive. CD-RW is a good choice when you need to store small amounts of
data over time, such as a daily backup of a few critical fi les. CD-R is more compatible with
stereo systems and other non-computer devices that play audio CDs, so it's a better choice
when burning a CD to which you don't expect to make changes.
In today's PCs, all writeable CD drives can read and write both CD-R and CD-RW
discs. CD-R blanks are less expensive than CD-RW blanks, so you may want to keep both
on hand for different usages.
PCs don't contain the manufacturing equipment to create the pitted aluminum layer that
exists on a mass-produced CD. The recording process for CD-R is made possible by the
fact that CD readers don't actually touch the surface of the disc—they only look at it. Thus
a home-recorded CD need not actually have the pits, as long as it appears to have them.
CD-R blanks have a dye-and-metal coating that is, in its natural state, very shiny. The laser
zaps certain areas of the disc to make it less shiny, and therefore less refl ective.
The CD drive's sensor interprets a less-refl ective area as a pit, regardless of whether the
area is actually pitted. Once a spot on a CD-R disc is made less refl ective, it can't be undone.
In contrast, CD-RW doesn't use a dye-and-metal coating. Instead it's coated with a metal
alloy with refl ective properties that change depending on the temperature to which it's heated.
Three settings are used. The high write setting heats the alloy to around 1,112 degrees
Fahrenheit, at which temperature it liquefi es. Then it solidifi es again and loses its refl ective
properties. The same spot can be reheated by the low write setting to a lower temperature
(around 392 degrees Fahrenheit), causing it to revert to its original refl ectivity. That is how an
area is rewritten. The lowest power setting reads the data without changing it.
DVD Drives
DVD stands for
Digital Versatile Disc
or
Digital Video Disc
. DVDs may look a lot like CDs,
but technologically they're much more advanced and hold much more data. DVD drives can
also read CDs, so it's rare to fi nd a CD-only drive these days; most optical drives can read
and write both CDs and DVDs.
