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Optical (CD/DVD) Drives
Description: Every modern PC contains an optical drive; the name refers to
the general category of disk drives that read information optically, using a low-powered
laser. CD-ROM drives were the first optical units commonly found on PCs; they began as
novelties for high-end users and grew in popularity as they dropped in price and increased
in performance, until the point arrived where they were mandatory equipment on any new PC
Today we have not just CD-ROM drives but their younger and higher-capacity siblings,
DVD drives. We also have writeable and rewriteable CD-ROM drives, called
CD-R and CD-RW respectively. These expand the capabilities of optical drives by letting
you actually write to CD-ROM media.
Tip: For additional information
on CD-ROM drives, including more discussion of many of the technical details, criteria and
features mentioned below, see the Reference Guide section
on CD-ROM drives.
Role and Subsystems: Optical drives are storage devices and part of the storage
subsystem. They usually interface either through the standard IDE/ATA controller ports on
the motherboard, or a SCSI interface host adapter. The optical drive in a system is an
important factor in the PC's ability to install and run software, since most software is
distributed on optical disks. In the case of writeable CD drives, they also are often the
only real backup devices in the PC.
Related Components: Optical drives are most closely related to the sound card, to
which they usually have some physical connection. They are also related to the motherboard
since they usually send data to the system through the motherboard. Most optical drives
are purchased to match the interface that has been chosen for the hard disk drive(s) in
the system, usually IDE/ATA or SCSI.
Key Compatibility Selection Criteria: Here are the key decisions that must be made
to select an optical drive:
- Drive Type: The first choice to make is whether you want a regular CD-ROM drive,
a DVD drive, or a writeable CD-RW drive. For a new system, I would recommend a DVD drive
over a CD-ROM drive, because the DVD can read all CD-ROM formats as well as DVD data and
video disks; CD-ROM drives can only read CD disks, not DVD. While most software still
comes in CD format, DVD will increase in popularity over time, and for a few dollars more
it's nice to have the flexibility. If you are on a budget though, you can get a CD-ROM
drive instead of DVD without losing too much capability, and upgrade later if and when you
feel it is worthwhile.
Then there is the matter of whether or not to get a writeable drive. The ability to write
really puts a CD-RW drive into a totally different "category" as it opens up a
lot of possibilities, such as doing backups, archiving data, or even recording your own
audio disks. Some high-end users get both a CD-RW and DVD drive since CD-RWs can't
generally read DVD disks, and DVD can't write CDs.
Note: CD-R drives, which can
write but not rewrite, have been largely pushed out of the market by CD-RW drives
that can do both operations. There are also several different types of writeable DVD
drives, but this market is still in its infancy and there are no widely-accepted standards
yet, so I would avoid these for now.
- Interface: The two most popular interfaces used for optical drives are the same
as the ones used for hard disk drives: IDE/ATA and SCSI (actually, IDE/ATA optical drives
technically use ATAPI, which is a variant of ATA, but they connect the same way as
hard drives). IDE/ATA is by far more popular, in large part due to the built-in support
that comes with virtually every motherboard. SCSI optical drives are popular for those who
already have SCSI systems, or who want the flexibility and expandability options SCSI
offers. SCSI has also traditionally been the interface of choice for CD-RW drives because
of the problems with data interruption associated with IDE/ATA, but this is changing
rapidly as PC systems increase in speed. For most users, IDE/ATA is acceptable for any
sort of optical drive, and certainly easier and cheaper.
- Loading Mechanism: The loading mechanism refers to the way that the disk
is loaded into the drive; there are three common types. The most popular is the
tray-loading drive, where a drawer-like tray comes out, you put the disk into it, and a
motor then closes the tray. Some higher-end systems use caddies, small carriers
into which you put the disk; some people consider them more durable and reliable, but the
drives are more expensive and you also have to buy the caddies, an extra cost. Finally,
some drives use a slot-loading mechanism similar to those that have been used for car CD
players for years. The choice is mainly one of preference.
Warning: If you are using a
tray-loading optical drive, be sure that when the system is placed in its final location,
the drive is oriented horizontally, or you won't be able to easily load disks. This is
usually only a problem for desktop cases that people try to stand on end like tower cases
to save desk space.
- Multi-Read Capability: For regular CD-ROM drives, this specification indicates
that the drive can read CD-RW media written by a CD-RW drive. (CD-RW disks have a lower
reflectance than conventional CDs.) Most newer CD-ROM drives have this capability, as do
all CD-RW and DVD drives.
- Digital Audio Extraction (DAE) Capability: All optical drives can play audio CDs,
but they differ greatly in their ability to extract digital audio from CDs to
computer data files. You need this capability if you want to work with digital audio files
or record your (legally purchased) music to MP3 format (for your own personal use, as I
do). If this is important to you, find out if the drive you are considering can do it, and
what the extraction speed is as well. Of course, for many people this is of no importance
whatsoever--which is one reason why some drives don't do it very well!
Performance and Capacity Selection Criteria: These are the most important
performance criteria for selecting an optical drive. As a preface to this long list, I
will point out that optical drive performance is just not that important to most PC
users; the reason is that most drives are already far faster than software usually
requires. (I discuss this more in the sections below). Here are the factors:
- "X" Rating: Optical drives are normally specified with an "X"
rating, intended to represent the speed of the drive. For example, a CD-ROM drive may be
specified as "40X", or a DVD drive as "6X". This is supposed to mean
that these units operate at 40 times and 6 times the speed of the first CD-ROM and DVD
drives, respectively. These "X" ratings do indicate approximate drive speed, but
they have become "magic numbers" and don't really represent as much of the
performance picture as you might think. See the discussion of "Magic Numbers"
below. (Note that the CD and DVD standards are different; a 1X DVD drive actually has
throughput of about eight times that of a 1X CD-ROM drive.)
- CLV vs. CAV: Traditional CD-ROM (and CD audio) drives vary the speed of the motor
depending on where on the disk data is being read, to keep the data throughput constant;
these are called constant linear velocity or CLV drives. Many newer CD-ROM
drives instead keep the motor the same speed; these are constant angular velocity
or CAV drives. The main difference between the two is that since CLV drives adjust
the motor speed, they have approximately the same transfer rate no matter where you read
on the surface of the disk; CAV drives have a higher transfer rate on the outside part of
the disk because the motor turns at a constant rate, and there is more data per revolution
on the outside of the disk. (There are also some drives that are hybrids, changing the
speed of the motor only over part of the surface.) The main reason why CAV drives were
developed is to increase speeds and thus transfer rates; at high speeds engineering CLV
drives is difficult.
Whatever, you may ask, why should I really care? Well, there's an important difference
between the drives. First, CAV drives (which are most common with high "X"
number drives today) read at their top speed only on the outside edge of the disk; on the
inside--which is where data is recorded first, mind you--they may be only half as fast.
CAV drives also usually spin much faster than CLVs, which is why they came to dominate the
market, but these higher spin speeds have negative quality effects; see below.
- Multiple-Beam Drives: A special technology called "TrueX", developed by
a company named Zen Research and popularized by Kenwood CD-ROM drives, uses new technology
to provide high transfer rates without requiring very fast spin speeds. Special hardware
is included to split the laser beam into seven "partial beams" that read seven
tracks at once. The drives are CLV and run at relatively low spin speeds, reducing
vibration and noise while providing the high transfer rates associated with drives that
spin at high speed.
- Access Time: Measured in milliseconds, access time is the amount of time that
elapses from the time a request is made to the optical drive until the data begins to be
read. It is a key performance measure. Be sure to find out the access time of any drive
you are considering; it can vary greatly between drives, even ones that have the same
- Transfer Rate: Transfer rate refers to how quickly data can be read from the
drive; it is indicated in rough terms by the drive's "X" rating and whether it
is a CLV, CAV or multiple-beam drive. Transfer rates (like "X" ratings) are
vastly over-rated for optical drives, because they are only important when you are copying
large amounts of data from the disk, which most people do rarely.
- Buffer Size: Like hard drives, optical drives have an integrated buffer that
improves performance slightly--and like hard drives, the importance of the size of the
buffer is overstated. The most important use of the buffer in an optical drive is for
CD-RW drives; the buffer on these units helps prevent bad CD-R burns caused by data not
being fed quickly enough to the drive by the system. For these units, buffer size is
important. For others, it really is not that important.
- Write Speed: CD-RW drives are usually specified using a notation such as this:
"12/4/32". This means the drive can write a CD-R (write-once) disk at 12X speed,
a CD-RW (rewriteable) disk at 4X speed, and read at 32X speed. All regular "X
rating" caveats apply, but faster speeds mean you can record data more quickly,
obviously. Here too, bear in mind that very high write speeds are only important if you
write a lot of data or music to CD-R; the difference between a 8X and 12X write
speed is only three minutes for an entire 650 MB CD-R.
- Spin-Up Delay: Very fast CAV units can spin their disks 10,000 RPM or even
higher! It takes time to get the drive up to this high speed, which can result in delays
when doing intermittent random accesses. (Most drives that spin at high speed reduce the
spin speed when the drive is idle to prevent motor burnout, and then you have to wait for
the drive to spin up again when you want to read.)
- DAE Speed: If you need to do a great deal of reading digital audio from audio
CDs, be sure to select a drive that does fast digital audio extraction (DAE). DAE speed
varies greatly from one model to another, and may have little to do with the speed at
which regular data is read by the drive. (For occasional audio extraction, even relatively
slow DAE is fine for most users.)
Quality Selection Criteria: The quality of optical drives receives far less
attention than it should, particularly considering how over-rated their performance is.
While most components in the PC world tend to improve in quality over time, CD-ROM drives
have in many ways gotten worse. As companies have fought to outdo each other with faster
and faster drives, some have created units that spin the disks so fast that very unsavory
side-effects are produced: noise, heat and vibration. Some drives are so bad that PC users
have been known to yank them out and put their older, slower CLV drives back in instead!
To avoid disappointment, evaluate using these basic factors:
- General Construction And Reputation: Look for feedback on optical drives before
buying, and avoid ones that have a reputation for noise, heat, or inconsistent operation.
Some companies have a long track record of producing high-quality optical drives, but
there are also lots of "no-name" firms producing drives that spin fast but do
- Spin Speed: In general, the faster the drive physically spins the disk, the more
issues there will be with noise, vibration, spin-up delay and so on.
- Vibration and Noise: Faster, lower-quality drives make a real racket when they
are operating and can create so much vibration that you can feel it through the table on
which the PC is sitting. Good drives produce less noise and vibration.
- DAE Quality: Drives differ not just in how quickly they can extract digital
audio, but also in how well. If you will do a lot of digital audio work, look for models
made by companies that have a good reputation for high-quality, error-free DAE, such as
Important Features: Most optical drives have fairly standardized features, but
there are a few extras to look for:
- Digital Audio Connection: To enable you to play audio CDs through your sound
card, all optical drives support the connection of a cable from the drive to a special
input jack on the sound card. This is an analog connection. In addition, some drives now
support a digital audio connection to compatible sound cards, to improve quality.
- Front Panel Controls: Some drives have some combination of the following on the
front, to enable playing audio CDs without software on the computer: headphone jack,
volume control, and start/stop/forward/reverse buttons. (All PCs with a sound card can
play audio CDs through the sound card.)
- 80-Minute CD-R Support: Standard CD-R blanks hold about 650 MB of data or 74
minutes of audio; there are also higher-capacity disks that will hold about 700 MB of data
or 80 minutes of audio. Only certain CD-RW drives support writing these.
"Magic Numbers" To Watch For: The "X" number used for rating
CD-ROM drives is one of the worst magic numbers in the PC world, because of the sheer
number of ways that it is deceptive. First of all, the "X" is supposed to refer
to the relative transfer rate, and it was accurate for CLV drives up to about 8X in speed.
Today, most drives used constant angular velocity, so they aren't in fact reading at the
rated throughput most of the time--only when reading the outermost parts of the disk.
Since disks are recorded from the inside out, much of the time the drive is running at
much less than its nominal speed.
More importantly, however, the "X" number only refers to the transfer rate of
the drive. Transfer rate is just not that important for most optical drive users. The
"X" read speed has no impact on using audio CDs or DVD movies, only data, and
most data is read in small pieces through random accesses, not long sequential reads. Few
people use optical drives enough that their performance is really all that critical.
The worst part of this particular magic number, however, is that it encourages people
to get faster drives they don't need, which are often of inferior quality to better-built,
somewhat slower units. A drive that costs $50 and claims to be "52X" may impress
you, but it's almost certain to be noisy, loud, create a lot of vibration, and take ages
to spin up to operating speed. (The "TrueX" drives being a notable exception.)
And those "extra Xes" aren't gaining you much anyway.
Performance Impact: The optical drive has relatively little overall performance
impact on the system, which is one of the reasons I make a point not to buy cheap,
high-RPM drives. It is important to certain types of users but doesn't affect the overall
performance of the system greatly unless you do a lot of reading from the disk, which
rarely occurs for most users.
Retail, OEM and Gray Market Issues: Optical drives are often sold as OEM units, and
gray market drives are also fairly common. I recommend retail units if possible as they
usually have a longer warranty and often come with useful software as well.
Importance of Manufacturer: High. I strongly recommend buying a reputable name
brand and avoiding the high-speed no-name drives that are often of dubious quality.
Typical Component Lifetime: Good-quality optical drives will last for many years; I
even have an old PC using a 2X CD-ROM drive with a manual tray (i.e., no motorized
mechanism to spit it out or pull it back in--you have to push it!) That thing must be a
decade old by now, or close. However, cheap CD-ROMs often fail quickly: burned out motors
and problems with the tray mechanism being the most common.
Obsolescence is really not a big deal in most cases; few software titles require
anything more than a 4X drive even today, and DVDs have been around for years without
making an appreciable change in the market as a whole.
Warranty Issues: A good-quality unit should come with at least a one-year warranty.
If you want to chance an OEM drive you'll probably be fine if you choose a good
Driver Support Issues: Drivers are not required for Windows to use regular optical
drives, but support issues abound for CD-RW drives. You need support for the particular
drive model from the various CD writing software packages. The best way to ensure this is
to stick to popular makes and models.
Special Specification Considerations: None that I can think of right now without
repeating stuff I've already said above. :^)
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