Hardware Reference
In-Depth Information
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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 2.0/3.0.
or i.LINK)
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Some older drives were available in external versions using SCSI/ASPI (Small Computer System
Interface/Advanced SCSI Programming Interface) or parallel printer port interfaces, 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 grab the hub of the
disc or tabs that fold in or flip over from the outside of the tray to retain the disc. If so, you can run the
drive in either a horizontal or a 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 requires that you
place the disc into a special caddy, which is a sealed container with a metal shutter. The caddy has a
hinged lid you open to insert the disc, but after that the lid remains 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.
Some drives use a slot-loading mechanism, identical to that used in most automotive players. This is
convenient because you just slip the disc into the slot, where the mechanism grabs it and draws it
inside. Some drives can load several discs at a time this way, holding them internally inside the drive
and switching discs as access is required.
The primary drawback to this type of mechanism is that if a jam occurs, it can be much more difficult
to repair because you might have to remove the drive to free the disc. Another drawback is that slot-
loading drives usually can't handle the smaller 80mm discs, card-shaped discs, or other modified
disc physical formats or shapes, such as DualDisc.
Other Drive Features
Although drive specifications are of the utmost importance, you should consider other factors and
features when evaluating optical drives. Besides quality of construction, the presence of drive sealing
or self-cleaning lenses bears scrutiny when you are making a purchasing decision.
Dirt is your drive's biggest enemy. Dust or dirt, when it collects on the lens portion of the mechanism,
