Hardware Reference
In-Depth Information
•
USB port
—Universal serial bus (USB) is normally used for external drives, and
provides benefits such as hot-swappability, which is the capability to be plugged in or
unplugged without removing the power or rebooting the system. USB 2.0 is the most
common, but USB 3.0 drives might be available in the future.
•
FireWire (IEEE 1394)
—A few external optical drives are available with a FireWire
(also called IEEE 1394 or i.LINK) interface instead of, or in addition to USB 2.0.
See
“
Universal Serial Bus (USB)
,”
p.
692
and “
IEEE 1394 (FireWire or i.LINK)
,
”
p.
707
(
Chapter 14
,
“
External I/O Interfaces
”
).
Some older drives were available in external versions using SCSI/ASPI (Small Computer
System Interface/Advanced SCSI Programming Interface) or parallel printer port inter-
faces, but these are obsolete.
Loading Mechanism
Three distinctly different mechanisms exist for loading a disc into an optical drive: the
tray, caddy, and slot.
Most current drives use a tray-loading mechanism. This is similar to the mechanism used
with a stereo system. Because you don't need to put each disc into a separate caddy, this
mechanism is much less expensive overall. However, it also means that you must handle
each disc every time you insert or remove it.
Some tray drives can't operate in a vertical (sideways) position because gravity prevents
proper loading and operation. Check to see whether the drive tray has retaining clips that
grabthehubofthediscortabsthatfoldinorflipoverfromtheoutsideofthetraytoretain
the disc. If so, you can run the drive in either a horizontal or vertical position.
The main advantage of the tray mechanism over the others is cost, and that is a big factor.
Most drives today use the tray mechanism for handling discs.
Caddy systems have been used on several types of optical drives. The caddy system re-
quiresthatyouplacethediscintoaspecialcaddy,whichisasealedcontainerwithametal
shutter. The caddy has a hinged lid you open to insert the disc, but after that the lid re-
mains shut. When you insert the caddy containing the disc into the drive, the drive opens
a metal shutter on the bottom of the caddy, allowing access to the disc by the laser.
The drawbacks to the caddy system include the expense and the inconvenience of having
to put the discs into the caddies. Caddy-loaded drives were popular in early CD drives,
but few were made or sold after 1994.
Somedrivesuseaslot-loadingmechanism,identicaltothatusedinmostautomotiveplay-
ers. This is convenient because you just slip the disc into the slot, where the mechanism
