This chapter explains the technology behind CD-ROM drives,
delineates the various recording formats used on PC CD-ROMs,
and examines the performance characteristics of the typical
CD-ROM drive. After showing you the process of selecting a
good drive for a system upgrade, the chapter guides you
through the installation of the CD-ROM interface card, the
drive itself, and the software that must be added to your PC
for the drive to communicate with the system. This chapter
also focuses on the latest CD technology, including brief
coverage of CD-R (CD-Recordable), CD-E (CD-Erasable), and the
new DVD (Digital Versatile Disk) drives.
NOTE: Detailed CD-R coverage can be found in
Chapter 18, "Tape and Other Mass-Storage Drives," because
its primary use for the average user is as a convenient way
to back up or store large amounts of data.
What Is a CD-ROM?
Within minutes of inserting a compact disc into your
computer, you have access to information that might have taken
you days, or even weeks, to find a few short years ago.
Science, medicine, law, business profiles, and educational
materials--every conceivable form of human endeavor or pursuit
of knowledge--are making their way to aluminum-coated,
five-inch plastic data discs called CD-ROMs, or
compact disc read-only memory.
NOTE: The CD-ROM (compact disc read-only
memory) is a read-only optical storage medium capable of
holding up to 682M of data (approximately 333,000 pages of
text), 74 minutes of high-fidelity audio, or some
combination of the two. The CD-ROM is very similar to the
familiar audio compact disc, and can, in fact, play in a
normal audio player. The result would be noise unless audio
accompanies the data on the CD-ROM (see the CD+ coverage
later in this chapter). Accessing data from a CD-ROM is
quite a bit faster than floppy disk but considerably slower
than a modern hard drive. The term CD-ROM refers to both the
discs themselves and the drive that reads them.
Although only a few dozen CD-ROM discs, or titles, were
published for personal computer users in all of 1988, there
are currently thousands of individual titles containing data
and programs ranging from world-wide agricultural statistics
to preschool learning games. Individual businesses, local and
federal government offices, and small businesses also publish
thousands of their own, limited-use titles.
CD-ROM, a Brief History
In 1978, Philips and Sony Corporations joined forces to
produce the current audio CD. Philips had already developed
commercial laser-disc players, whereas Sony had a decade of
digital recording research under its belt. The two companies
were poised for a battle--the introduction of potentially
incompatible audio laser disc formats--when they came to terms
on an agreement to formulate a single audio technology.
Sony pushed for a 12-inch platter. Philips wanted to
investigate smaller sizes, especially when it became clear
that they could pack an astonishing 12 hours of music on the
12-inch discs.
By 1982, the companies announced the standard, which
included the specifications for recording, sampling,
and--above all--the 4.72-inch format we live with today. To be
specific, the discs are precisely 120mm in diameter, have a
15mm hole in the center, and are 1.2mm thick. This size was
chosen (legend has it) because it could contain Beethoven's
Ninth Symphony.
With the continued cooperation of Sony and Philips through
the 1980s, additional specifications were announced concerning
the use of CD technology for computer data. These
recommendations evolved into the computer CD-ROM drives in use
today. Where once engineers struggled to find the perfect fit
between disc form-factor and the greatest symphony ever
recorded, software developers and publishers are cramming
these little discs with the world's information.
CD Technology
Although identical in appearance to audio CDs, computer CDs
store data in addition to audio. The CD drives that read the
data discs when attached to PCs also bear a strong resemblance
to an audio CD. How you must handle the CDs (insert them into
the CD drive and eject them when finished) is already familiar
to anyone who has used an audio CD. Both forms of CD operate
on the same general mechanical principles.
The disc itself, 120mm (nearly 4.75 inches in diameter), is
made of a polycarbonate wafer. This wafer base is coated with
a metallic film, usually an aluminum alloy. The aluminum film
is the portion of the disc that the CD-ROM drive reads for
information. The aluminum film or strata is then
covered by a plastic polycarbonate coating that protects the
underlying data. A label is usually placed on the top of the
disc, and all reading occurs from the bottom. CD-ROMs are
single-sided.
NOTE: CD-ROM media should be handled with the
same care afforded a photographic negative. The CD-ROM is an
optical device and it degrades as its optical surface
becomes dirty or scratched. If your drive uses a caddy--a
container for the disc that does not require handling the
disc itself--you should purchase a sufficient supply of
these to reduce disc handling.
Mass-Producing CD-ROMs Although a laser is used to
etch data onto a master disc, this technique would be
impractical for the reproduction of hundreds or thousands of
copies. Each production of a master disc can take over
one-half hour to encode. In addition, these master discs are
made of materials that aren't as durable as a mass-produced
disc for continued or prolonged use. For limited run
productions of CDs, an original master is coated with metal
in a process similar to electroplating. After the metal is
formed and separated from the master, the metal imprint of
the original can be used to stamp copies, not unlike the
reproduction of vinyl records. This process works
effectively for small quantities; eventually the stamp wears
out.
To produce a large volume of discs, the following
three-step process is employed:
1. The master is, once again, plated and a stamp
is produced.
2. This stamp is used to create a duplicate master
made of a more resilient metal.
3. The duplicate master then can be used to
produce numerous stamps.
This technique allows a great many production stamps to
be made from the duplicate master, preserving the original
integrity of the first encoding. It also allows for the mass
production to be made from inexpensive materials. The CDs
you buy are coated with aluminum after they are stamped into
polycarbonate and then protected with a thin layer of
plastic. The thin, aluminum layer that coats the etched
pits, as well as smooth surfaces, enables the reading laser
to determine the presence or absence of strongly relented
light.
This mass manufacturing process is identical for both
data and audio CDs.
Reading the information back is a matter of reflecting a
lower-powered laser off the aluminum strata. A receiver or
light receptor notes where light is strongly reflected or
where it is absent or diffused. Diffused or absent light is
caused by the pits etched in the CD. Strong reflection of the
light indicates no pit--this is called a land. The
light receptors within the player collect the reflected and
diffused light as it is refracted from the surface. As the
light sources are collected from the refraction, they are
passed along to microprocessors that translate the light
patterns back into data or sound.
Individual pits are 0.12 microns deep and about 0.6 microns
wide. They are etched into a spiral track with a spacing of
1.6 microns between turns, corresponding to a track density of
nearly 16,000 tracks per inch! The pits and lands run from 0.9
to 3.3 microns long. The track starts at the inside of the
disc and ends as close as 5mm from the edge of the disc. This
single spiral track is nearly three miles long!
When a CD--audio or data--seeks out a bit of data on the
disc, it looks up the address of the data from a table of
contents and positions itself near the beginning of this data
across the spiral, waiting for the right string of bits to
flow past the laser beam.
CD-ROM data is recorded using a technique called
Constant Linear Velocity (CLV). This means that the
track data is always moving past the read laser at the same
linear speed. In other words, the disk must spin faster when
reading the inner track area and slower when reading the outer
track area. Because CDs were originally designed to record
audio, the speed at which the data was read had to be a
constant. Thus each disc is broken up into blocks, or sectors,
which are stored at the rate of 75 blocks per second on a disc
that can hold a total of 74 minutes of information, resulting
in a maximum of 333,000 blocks (sectors).
New multispeed CD-ROM readers still read the same CLV
recorded CDs, but they play them back at a Constant Angular
Velocity (CAV). This means that the track data is moving
past the read laser at a different speed, depending on where
the track is physically located on the CD (inner or outer
track). Tracks at the edge of the disk are read faster than
ones near the center, because the CD is rotating at a constant
speed, similar to old record players. A combination of these
two technologies is referred to as P-CAV or
Partial-CAV.
In a CD-DA (Digital Audio) disc, each block stores 2,352
bytes. In a CD-ROM disc, 304 of these bytes are used for Sync
(Synchronizing bits), ID (Identification bits), and ECC (Error
Correcting Code) information, leaving 2,048 bytes for user
data. Because these blocks are read at a constant speed of 75
per second, this results in a standard CD-ROM transfer rate of
153,600 bytes per second, which is exactly 150K/sec.
Because a disc can hold a maximum of 74 minutes of data,
and each second contains 75 blocks of 2,048 bytes each, one
can calculate the absolute maximum storage capacity of a
CD-ROM at 681,984,000 bytes.
NOTE: Recordable CDs come in 74-minute and
63-minute versions.
Inside Data CDs
The microprocessor that decodes the electrical impulses is
the key difference between music and data compact players.
Audio CDs convert the digital information stored on the disc
into analog signals for a stereo amplifier to process. In this
scheme, some imprecision is acceptable, because it would be
virtually impossible to hear in the music. CD-ROMs, however,
cannot tolerate any imprecision. Each bit of data must be
accurately read. For this reason, CD-ROM discs have a great
deal of additional ECC (Error Correcting Code)
information written to the disc. The ECC can be used to detect
and correct most minor errors, improving the reliability and
precision to levels that are acceptable for data storage.
CD-ROM drives operate in the following manner:
- 1. The laser diode (see Figure 17.1) emits
a low-energy infrared beam toward a reflecting mirror.
2. The servo motor, on command from the
microprocessor, positions the beam onto the correct track on
the CD-ROM by moving the reflecting mirror.
3. When the beam hits the disc, its refracted
light is gathered and focused through the first lens beneath
the platter, bounced off the mirror, and sent toward the
beam splitter.
4. The beam splitter directs the returning
laser light toward another focusing lens.
5. The last lens directs the light beam to a photo
detector that converts the light into electric impulses.
6. These incoming impulses are decoded by the
microprocessor and sent along to the host computer as data.
FIG.
17.1 Typical components inside a
CD-ROM drive.
The pits that are etched into the CD-ROM vary in length.
The reflected light beam changes in intensity as it crosses
over from a land to a pit area. The corresponding electrical
signal from the photodetector varies with the reflected light
intensity. Data bits are read as the transitions between high
and low signals, which is physically recorded at the start and
end of each pit area.
Because a single bit error can be disastrous in a program
or data file, extensive error detection and correction
algorithms are utilized. These routines allow for the
probability of a nondetected error to be less than 1 in
1025. In more physical terms, this means that there
would be only one undetected error in 2 quadrillion discs
(this would form a stack 1 billion miles high!).
Error correction alone requires 288 bytes for every 2,048
bytes of disc data. This allows for the correction of numerous
bad bits, including bursts of bad data more than 1,000 bits
long. This powerful error-correction capability is required
because physical defects can cause errors, and because the CD
media was originally designed for audio reproduction where
minor errors or even missing data can be tolerated.
In the case of an audio CD, missing data can be
interpolated--that is, the information follows a
predictable pattern that allows the missing value to be
guessed at. For example, if three values are stored on an
audio disc, say 10, 13, and 20 appearing in a series, and the
middle value is missing--due to damage or dirt on the CD's
surface--you can interpolate a middle value of 15, which is
midway between the 10 and 20 values. Although this is not
exactly correct, in the case of audio recording, it will not
be noticeable to the listener. If those same three values
appear on a CD-ROM in an executable program, there is no way
to guess at the correct value for the middle sample.
Interpolation cannot work because executable program data
follows no natural law; the data is a series of values. To
guess 15 is not just slightly off, it is completely wrong.
Because of the need for such precision, CD-ROM drives for
use on PCs were later to market than their audio counterparts.
When first introduced, CD-ROM drives were too expensive for
widespread adoption. In addition, drive manufacturers were
slow in adopting standards, causing a lag time for the
production of CD-ROM titles. Without a wide base of software
to drive the industry, acceptance was slow.
What Types of Drives Are
Available?
When purchasing a CD-ROM drive for your PC, consider three
distinct sets of attributes of CD-ROM drives, as follows:
- The drive's performance specifications
- The interface it requires for connection to your
PC
- The physical disc-handling system used
The variance in any of these categories is enormous; in
fact, single vendors offer entire lines of drives that vary in
performance specifications, disc-handling mechanisms, and type
of adapters they can use to interface with your PC. For these
reasons, drive prices vary widely. CD-DA (Compact Disc-Digital
Audio) drives, for example, are very inexpensive because they
don't require the precision in reproducing music that is
required by a drive used for storing data. So before you buy,
know the drive's characteristics.
All three drive characteristics are discussed in this
section, giving you a better understanding of what type of
drive you need to buy.
CD-ROM Drive Specifications
Drive specifications tell you the drive's performance
capabilities. If you're shopping for a sports car, for
example, and the dealer tells you the car can accelerate from
a standing stop to 60 miles per hour in five seconds, you know
you've got a hot car. The car's horsepower, weight, suspension
design, and other specifications can be used to understand the
vehicle's performance.
CD-ROM drive specifications tell the shopper much the same
thing. Typical performance figures published by manufacturers
are the data transfer rate, access time, internal cache or
buffers (if any), and the interface used.
Data Transfer Rate.
The data transfer rate tells you how much data the drive
can read from a data CD and transfer to the host computer when
reading one large, sequential chunk of data. The standard
measurement in the industry is kilobytes per second, usually
abbreviated as K/sec. If a manufacturer claims a drive can
transfer data at 150K/sec, it means that a drive reading a
sequential stream of data from the CD will achieve 150K/sec
after it has come up to speed. Note that this is a sustained
and sequential read, not access across the data disc from
different portions of the platter. Obviously, the data
transfer specification is meant to convey the drive's peak
data-reading capabilities. A higher rate of transfer might be
better, but a number of other factors come into play.
You can obtain a CD-ROM benchmark tool by visiting TestaCD
Labs Web site at the following:
http:/www.azstarnet.com/~gcs/
The standard CD format dictates that there are 75 blocks
(or sectors) of data per second, with each block containing
2,048 bytes of data. This gives a transfer rate of exactly
150K/sec. This is the standard for CD-DA (Digital Audio)
drives, and also is called Single-speed in CD-ROM
drives. The term Single-speed is used to refer to the
original 150K/sec drives, because CD discs are recorded in a
Constant Linear Velocity (CLV) format, which means that
the rotational speed of the disc will vary to keep the track
speed a constant. A Double-speed drive (or 2x) simply attains
a transfer rate of 300K/sec or two times the single-speed
drive.
Because CD-ROM drives can read data that is not time-based
like audio, it is possible to speed up the reading of these
discs by spinning them at a higher linear velocity. There are
currently several different speed drives available, all of
which are multiples of the original Single-speed drives. Table
17.1 shows the speeds at which CD-ROM drives can operate.
Table 17.1 CD-ROM Drive Speeds and Data
Transfer Rates
Drive Speed |
Transfer Rate (bps) |
Transfer Rate (K/sec) |
Single-speed (1x) |
153,600 |
150 |
Double-speed (2x) |
307,200 |
300 |
Triple-speed (3x) |
460,800 |
450 |
Quad-speed (4x) |
614,400 |
600 |
Six-speed (6x) |
921,600 |
900 |
Eight-speed (8x) |
1,228,800 |
1,200 |
Ten-speed (10x) |
1,536,000 |
1,500 |
Twelve-speed (12x) |
1,843,200 |
1,800 |
Sixteen-speed (16x) |
2,457,600 |
2,400 |
CAV drives (12x-24x) |
1,843,200-3,686,400 |
1,800-3,600 | bps =
bytes per second K/sec = kilobytes per second
The 10x and 12x drives currently are the most popular, and
the 4x drives are the minimum recommended today which meet the
new MPC-3 (Multimedia Personal Computer) standard. There are
some 16x (sixteen-speed) drives on the market now, but they
are already being overshadowed by the CAV 12/24x (multispeed)
drives in popularity. Unless you are using a laptop system,
the 16x drives are not recommended, as they cost more than 12x
drives, yet do not offer a significant overall jump in
performance to be worthwhile. For laptop multimedia computers
with integrated CD-ROM drives, 8x drives are quite popular;
however, for desktop systems, the 10x drives were quickly
passed over by cheaper 12x drives, just as the 3x drives were
passed over by cheaper 4x units. For an increase to be
worthwhile, it should be double the previous standard. It
remains to be seen how the CAV 12/24x drives will fare in the
marketplace.
Even the fastest CD-ROM drives pale in comparison to hard
disk drive transfer rates, which can obtain 16M or more per
second. This means that the SCSI or ATA-IDE interfaces used by
CD-ROM drives are more than up to-the-task. If you expect to
run a variety of CD-based software on your system, you need a
drive with a high data transfer rate. Applications that employ
full-motion video, animation, and sound require high transfer
rates, and you'll be disappointed in the results of a slower
drive. The minimum recommended drive should be a Quad-speed
drive, which means it can transfer data at a rate of
600K/sec.
Access Time
The access time for a CD-ROM drive is measured the same way
for PC hard drives. In other words, the access time is
the delay between the drive receiving the command to read, and
its actual first reading of a bit of data. The time is
recorded in milli- seconds; a typical manufacturer's rating
for a Quad-speed drive would be listed as 200ms. This is an
average access rate; the true access rate
depends entirely on where the data is located on the disc.
Positioning the read mechanism to a portion of the disc near
the narrower center of the disc gives you a faster access rate
than positioning it at the wider outer perimeter. Access rates
quoted by many manufacturers are an average taken by
calculating a series of random reads from a disc.
Obviously, a faster average access rate is desirable,
especially when you are relying on the drive to locate and
pull up data quickly. Access times for CD-ROM drives are
steadily improving, and the advancements are discussed later
in this chapter. Note that these average times are
significantly slower than PC hard drives, ranging from 500 to
100ms when compared to 8ms found on your typical hard disk.
Most of the speed difference lies in the construction of the
drive itself; hard drives have multiple read heads and range
over a smaller surface area of media. CD-ROM drives have only
one laser read beam, and it must be positioned over the entire
range of the disc. In addition, the data on a CD is organized
in a long spiral from the outer edge inward. When the drive
positions its head to read a track, it must estimate the
distance into the disc and skip forward or backward to the
appropriate point in the spiral. Reading off the outer edge
requires a longer access time than the inner segments, unless
you have a CAV drive, which spins at a constant rate so outer
tracks have equal access time to inner tracks.
Access times have been falling since the original
Single-speed drives came out. With each subsequent boost in
data transfer speed, we usually have also seen an increase in
access time as well. As you can see in Table 17.2, any
improvements here are much less significant, as you are seeing
the physical limitation of the drive's single-read mechanism
design.
Table 17.2 Typical CD-ROM Drive Access
Times
Drive Speed |
Access Time (ms) |
Single-speed (1x) |
400 |
Double-speed (2x) |
300 |
Triple-speed (3x) |
200 |
Quad-speed (4x) |
150 |
Six-speed (6x) |
150 |
Eight-speed (8x) |
100 |
Ten-speed (8x) |
100 |
Twelve-speed (12x) |
100 |
Sixteen-speed (16x) |
90 |
CAV (12/24x) |
150-90 |
The times listed here are typical examples for good drives;
within each speed category there will be drives that are
faster and slower.
Buffer/Cache
Most drives are shipped with internal buffers or caches of
memory installed on-board. These buffers are actual
memory chips installed on the drive's board that enable data
to be staged or stored in larger segments before they are sent
to the PC. A typical buffer for a CD-ROM drive is 256K,
although drives are available that have either more or less
(more is usually better!). Generally, the faster drives come
with more buffer to handle the higher transfer rates.
Having buffer or cache memory on the CD-ROM drive offers a
number of advantages. Buffers can ensure that the PC receives
data at a constant rate; when an application requests data
from the CD-ROM disc, the data is probably scattered across
different segments of the disc. Because the drive has a
relatively slow access time, the pauses between data reads can
cause a drive to send data to the PC sporadically. You might
not notice this in typical text applications, but a slower
access rate drive coupled with no data buffering is very
noticeable, even irritating, in the display of video or some
audio segments. In addition, a drive's buffer, when under
control of sophisticated software, can read and have ready the
disc's table of contents, making the first request for data
faster to find on the disc platter. A minimum size of 256K for
a built-in buffer or cache is recommended, which is standard
on most Eight-speed drives.
Interface
A CD-ROM's interface is the physical connection of
the drive to the PC's expansion bus. The interface is the
pipeline of data from the drive to the computer, and its
importance shouldn't be minimized. There are three different
types of interfaces available for attaching a CD-ROM drive to
your system. They are:
- SCSI/ASPI (Small Computer System Interface, Advanced
SCSI Programming Interface)
- IDE/ATAPI (Integrated Drive Electronics/AT Attachment
Packet Interface)
- Proprietary
This next section examines these different interface
choices.
SCSI/ASPI
SCSI (pronounced SKUH-zee), or the Small Computer
System Interface, is a name given to a special interface
bus that enables many different types of peripherals to
communicate. The current implemented version of the standard
is called SCSI-2. A standard software interface called
ASPI (Advanced SCSI Programming Interface) is
most commonly used to communicate between the CD-ROM drive (or
other SCSI peripherals) and the host adapter. SCSI offers the
greatest flexibility and performance of the interfaces
available for CD-ROM drives and can be used to connect many
other types of peripherals to your system as well.
The SCSI bus enables computer users to string a group of
devices along a chain from one SCSI host adapter, avoiding the
complication of inserting a different adapter card into the PC
bus slots every time a new hardware device, such as a tape
unit or additional CD-ROM drive, is added to the system. These
traits make SCSI interfaces preferable for connecting
peripherals such as your CD-ROM to your PC.
All SCSI adapters are not created equal, however. Although
they may share a common command set, they can implement these
commands differently, depending on how the adapter's
manufacturer designed the hardware. To eliminate these
incompatibilities, ASPI was created. ASPI stands for Advanced
SCSI Programming Interface and was originally developed by
Adaptec, Inc. (Adaptec SCSI Interface), a leader in the
development of SCSI controller cards and adapters. ASPI
consists of two main parts. The primary part is an
ASPI-Manager program, which is a driver that is written to
work between the particular operating system used and the
specific SCSI host adapter. The ASPI-Manager sets up the ASPI
interface to the SCSI bus.
The second part of an ASPI system is the individual ASPI
device drivers. For example, you would get an ASPI driver for
your SCSI CD-ROM drive. You also can get ASPI drivers for your
other SCSI peripherals such as tape drives, scanners, and so
on. The ASPI driver for the peripheral talks to the
ASPI-Manager for the host adapter. This is what allows the
devices to communicate together on the SCSI bus.
The bottom line is that if you are getting a SCSI interface
CD-ROM, make sure that it includes an ASPI driver that runs
under your particular operating system. Also, be sure that
your SCSI host adapter has the corresponding ASPI-Manager
driver as well.
You can visit Adaptec's home page on the Web at:
http://www.adaptec.com
The SCSI interface offers the most powerful and flexible
connection for CD-ROMs and other devices. It allows for higher
performance, and up to seven or more drives can be connected
to a single host adapter. The drawback is cost. If you do not
need SCSI for other peripherals, and if you intend on
connecting only one CD-ROM drive to the SCSI bus, then you
will be spending a lot of money on unused potential. In that
case, an IDE/ATAPI interface CD-ROM drive would be a more
cost-effective choice.
IDE/ATAPI.
The IDE/ATAPI (Integrated Drive Electronics/AT
Attachment Packet Interface) is an extension of the same
ATA (AT Attachment) interface most people connect their hard
disk drives to. Specifically, ATAPI is an industry standard
Enhanced IDE interface for CD-ROM drives. ATAPI is a software
interface that adapts the SCSI/ASPI commands to the IDE/ATA
interface. This has allowed drive manufacturers to take their
high-end CD-ROM drive products and quickly adapt them to the
IDE interface. This also allows the IDE CD-ROM drives to
remain compatible with the MSCDEX (Microsoft CD-ROM
Extensions) that are used to interface with DOS. With Windows
95, the CD-ROM extensions are contained in the CDFS (CD File
System) VxD (virtual device) driver.
ATAPI drives are sometimes also called Enhanced IDE drives,
because this is an extension of the original IDE (technically
the ATA) interface. In most cases, an IDE/ATA CD-ROM drive
will connect to the system via a second IDE interface
connector and channel, leaving the primary one for hard disk
drives only. This is done because IDE does not share the
single channel well, and would cause the hard disk to wait for
CD-ROM commands to complete and vice versa. SCSI does not have
this problem because you can send commands to different
devices without having to wait for each previous command to
complete.
The IDE/ATAPI interface represents the most cost-effective,
yet high performance interface for CD-ROM drives. Most new
systems that include a CD-ROM drive have it connected through
IDE/ATAPI. To prevent performance problems, be sure that your
CD-ROM drive is connected on a secondary IDE channel that is
separate from the primary channel used by your hard disk
drive. Many sound cards now include an ATAPI interface driver
and the requisite secondary IDE interface connector
specifically for a CD-ROM drive. Up to two drives can be
connected to the secondary IDE connector, but for more than
that, SCSI would be a better choice.
Proprietary Interfaces
The last type of interface you might see for CD-ROM drives
is the proprietary interfaces. These are often included
in the very low cost CD-ROM drive kits that come with their
own adapter card. These interfaces are nonstandard and
although inexpensive, are not flexible and do not offer high
performance. It is recommended that you stay away from any of
the proprietary CD-ROM interfaces and only use drives that
interface via SCSI or IDE/ATAPI.
Loading Mechanism
There are two distinctly different mechanisms for loading a
CD into a CD-ROM drive. They are the caddy and the
tray. Each one offers some benefits and features. Which
type you select will have a major impact on your use of the
drive because you will interact with this every time you load
a disc.
There are some multiple disc drives on the market now that
enable you to insert more than one disc at a time. Most of
these use a special cartridge that you fill with discs, much
like a multidisc player for automotive use.
Caddy
The caddy system is used on most high-end CD-ROM
drives. This system r requires that you place the CD itself
into a special caddy, which is a sealed container with a metal
shutter. The caddy has a hinged lid that enables you to open
it for inserting the CD, but after that the lid remains shut.
When you insert the caddy containing the CD into the drive,
the drive will open a metal shutter on the caddy, allowing
access to the CD by the laser.
The caddy is not the most convenient loading mechanism.
Although, if all of your CDs are in their own caddies, then
all you have to do is grab the caddy containing the disc you
want and shove it into the drive. This makes the CD operate
much like a 3 1/2-inch disk. You can handle the caddy without
worrying about touching or contaminating the disc or the
drive, making this the most accurate and durable mechanism as
well. Young children can easily handle the caddies and don't
have to touch the delicate CD discs themselves.
Because the caddy is sealed, the discs are protected from
damage caused by handling. The only time the disc is actually
handled is when it is first put into the caddy. The caddy
loading system also ensures that the disc is properly located
when inside the drive. This allows for more accurate laser
head positioning mechanisms, and caddy drives generally have
faster access times as well.
The real drawback to the caddy is the expense. You only get
one caddy with the drive, so you need to buy many more.
Otherwise, each time you insert a new disc into the drive, you
first have to eject the caddy/disc, remove the disc from the
caddy, put the disc back into the original jewel case, open
the jewel case for the new disc, put the new disc into the
caddy, and finally insert the caddy/disc back into the drive.
Caddies cost about $3 each, and it is recommended that you
have at least 20 or so on hand, or at least as many as you
have discs that you regularly use. Of course this will add $60
or more to the cost of your CD-ROM drive, but that is the
price you pay for convenience, durability, reliability, and
higher performance.
After you have caddies for all of your discs, the disc swap
procedure is much easier--simply eject the one in the drive,
grab the new caddy/disc and shove it back in! The caddy
essentially takes the place of the jewel case, and the disc
should be left in the caddy permanently.
A final advantage of caddy-loaded drives is that they can
be mounted in either a horizontal or vertical plane, meaning
that the drive can be installed sideways. This cannot be done
with the cheaper tray-loaded drives, but newer tray-loaded
drives have small retaining tabs that allow both horizontal or
vertical mounting.
Tray
Most drives use a tray loading mechanism. This is
similar to the CD-DA (Digital Audio) drive used with your
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 have to handle each disc every
time you insert or remove it.
Tray loading is more convenient than a caddy system,
because you don't need a caddy. However, this can make it much
more difficult for young children to use the discs without
smudging or damaging them due to the excessive handling.
The tray loader itself also is subject to damage. The trays
can be easily broken if they are bumped or if something is
dropped on them while they are extended. Also, any
contamination you place on the tray or disc is brought right
into the drive when the tray is retracted. Tray-loaded drives
should not be used in a harsh environment, such as a
commercial or industrial establishment.
The tray mechanism also does not hold the disc as securely
as the caddy. If you don't have the disc placed in the tray
properly when it is retracted, then the disc or tray can be
damaged. Some tray drives cannot be run in a vertical
(sideways) position, as gravity would prevent proper loading
and operation. Check to see if the drive tray has retaining
clips on the outer edge of the CD seat, like the Hitachi drive
I have in my HP Vectra. If so, you can run the drive in either
horizontal or vertical position.
The real advantage to the tray mechanism over the caddy
system is in cost, and that is a big factor. If you do not
have young children and the drive will be run in a clean
environment where careful handling and cleanliness can be
assured, then the tray mechanism would be recommend due to its
significantly lower cost.
Other Drive Features
Although drive specifications are of the utmost importance,
other factors and features should be taken into consideration
as well. Besides quality of construction, the following
criteria bear scrutiny when making a purchase decision:
- Drive sealing
- Self-cleaning lenses
- Internal versus external drive
Drive Sealing
Dirt is your CD-ROM's biggest enemy. Dust or dirt, when it
collects on the lens portion of the mechanism, can cause read
errors or severe performance loss. Many manufacturers seal the
lens and internal components in airtight enclosures from the
drive bay. Other drives, although not sealed, have double dust
doors--one external and one internal--to keep dust from the
inside of the drive. All these features help prolong the life
of your drive.
Caddy-loaded drives are inherently sealed better and are
much more resistant to the external environment than
tray-loaded drives. Always use a caddy-loaded drive in harsh
industrial or commercial environments.
Self-Cleaning Lenses
If the laser lens gets dirty, so does your data. The drive
will spend a great deal of time seeking and reseeking, or
finally giving up. Lens cleaning discs are available, but
built-in cleaning mechanisms are now included on virtually all
good quality drives. This may be a feature you'll want to
consider, particularly if you work in a less- than-pristine
work environment, or you have trouble keeping your desk clean,
let alone your CD-ROM drive lens.
Internal versus External Drives
When deciding whether you want an internal or external
drive, think about where and how you're going to use your
CD-ROM drive. What about the future expansion of your system?
Both types of drives have advantages and disadvantages. The
following lists some of the issues:
- External Enclosure. These tend to be rugged,
portable, and large--in comparison to their internal
versions. Buy an external one only if you lack the space
inside the system. You might also consider an external if
you want to move the drive from one PC to another easily. If
each PC has its own SCSI adapter, all you need to do is
unplug the drive from one adapter and plug it in to the
other. Only SCSI CD-ROM drives can be external, so if you
are looking for an IDE type interface, you must go
internal.
- Internal Enclosure. Internal drives will clear
off a portion of your desk. Buy an internal drive if you
have a free drive bay, or plan on keeping the CD-ROM drive
exclusively on one machine. All modern PCs should have a
CD-ROM drive; it is no longer looked at as a peripheral. The
internal drives are nice because you can connect the audio
connector to your sound card and leave the external audio
connectors free for other inputs. Internal drives can be IDE
or SCSI.
CD-ROM Disc and Drive Formats
Compact discs are pitted to encode the binary bits of 0 and
1. Without this logical organization to this disc full of
digits, the CD-ROM drive and PC would be at a loss to find any
discernible data amid all those numbers. To this end, the data
is encoded to conform to particular standards. When a drive
encounters particular patterns, it--and the PC--can recognize
the organization of the disc and find its way around the
platter. Without standard data formats, the CD-ROM industry
would be dead in the water; vendors of particular discs and
disc drives would be producing incompatible software discs and
drives, and thereby limiting the number of units that could be
sold.
Formats are also needed to advance the technology. For
example, hard rubber wheels and no suspension were just fine
for the first automobiles as they cruised along at the
break-neck speed of 30 miles an hour. But hitting a pothole at
60 mph could cause serious damage to the vehicle--and the
riders. Inflatable tires and shock absorbers became necessary
components of the modern car.
Similarly, the standards for disc formats evolved as well.
The first compact data discs stored only text information,
which was relatively easy to encode onto a disc. Graphics
produced a greater challenge, and the standards evolved to
incorporate them. The use of animation with synchronized
sound, and then live-motion video, called for other expansions
to the standards in which CDs store data.
It is extremely important to note that advanced CD-ROM
standards are in the process of evolution right now. Multiple
vendors are deploying a number of different techniques for
expanding the capabilities of CD-ROM technology. They may be
incompatible with each other or immature in their development,
but acceptance of these newer standards by software vendors is
essential to the widespread use of these standards. It is
important that you are familiar with these issues before you
purchase a drive; consider the formats it is capable of
reading now--and in the future.
The majority of drives available today, however, do comply
with earlier CD-ROM formats, ensuring that the vast library of
CD-ROM applications available today can be used on these
drives.
Data Standard: ISO 9660
Manufacturers of the first CD-ROM data discs produced their
discs for one particular drive. In other words, a data disc
produced for company A's drive could not be read by anyone who
had purchased company B's CD-ROM drive--the disc needed to be
formatted for each manufacturer's drive. Obviously, this
stalled the development of the industry. Philips and Sony
developed the "Yellow Book" specifications for data
CD-ROMs.
When Philips and Sony first published the audio CD
specifications, the material was released in a red binder and
became known as the "Red Book." Subsequent CD-ROM
specifications have been dubbed by color as well, such as the
"Orange Book" and the "Green Book."
An extension of the way in which audio data was stored on
disc, the Yellow Book specifications detail how data--rather
than audio--can be organized on a disc for its later
retrieval. The International Standards Organization
(ISO) refined this specification (called ISO 9660) in
such a way that every vendor's drive and disc would expect to
find a table of contents for a data disc. This is known as a
Volume Table of Contents, and it really is quite
similar to a standard book's table of contents in theory. ISO
9660 did not completely solve compatibility problems, however.
The incorporation of additional data to aid and refine the
search for data on a disc, and even how to format the data
blocks were still left to each separate vendor's design.
High Sierra Format
It was in all manufacturers' interests to resolve this
issue. In a meeting in 1985 at the High Sierra Hotel and
Casino in Lake Tahoe, California, leading manufacturers of
CD-ROM drives and CD-ROM discs came together to resolve the
differences in their implementation of the ISO 9660 format.
The agreement has become known as the High Sierra
format and is now a part of the ISO 9660 specification
document. This expansion enabled all drives to read all ISO
9660-compliant discs, opening the way for the mass production
of CD-ROM software publishing. Adoption of this standard also
enabled disc publishers to provide cross-platform support for
their software, easily manufacturing discs for DOS, UNIX, and
other operating system formats. Without this agreement, the
maturation of the CD-ROM marketplace would have taken years
longer and stifled the production of available CD ROM-based
information.
The exact and entire specifications for how to format the
CD media are complex, strewn with jargon you may never need,
and superfluous to your understanding of drive capabilities.
You should know the basics, however, because it gives you a
glimpse of the inner workings of retrieving data so quickly
from such an enormous well.
To put the basic High Sierra format in perspective, the
disc layout is roughly analogous to a floppy disk. A floppy
has a system track that not only identifies itself as a floppy
and its density and operating system, but also tells the
computer how it's organized--into directories, which are made
up of files.
Basic CD-ROM formats are much the same. The initial track
of a data CD identifies itself as a CD and begins
synchronization between the drive and the disc. Beyond the
synchronization lies a system level that details how the
entire disc is structured; as a part of the system area, the
disc identifies the location of the volume area--where the
actual data is held. The system also contains the directories
of this volume, with pointers or addresses to various named
areas, as illustrated in Figure 17.2. A significant difference
between CD directory structures and that of DOS is that the
system area also contains direct addresses of files within
their subdirectories, allowing the CD to seek to a specific
location on the spiral data track.
Because the CD data is all really on one, long, spiral
track, when speaking of tracks in the context of a CD, we're
talking about sectors or segments of data along the
spiral.
FIG.
17.2 A diagram of CD-ROM basic
file organizational format.
CD-DA (Digital Audio)
Data drives that can read data and audio are called
CD-DA. Virtually any data drive now being sold reads
both types of discs. When you insert a disc, the drive reads
the first track of the disc to determine what type you loaded.
Most drives ship with audio CD software, which enables you to
play music CDs from your PC. You can use headphones, or with
an installed sound card, connect speakers to the system. Some
external drives ship with standard Left/Right audio plugs;
just plug them into any external amplifier.
CD+
Philips and Sony have recently introduced a new CD format
called CD+. This is a new format that enables audio CD players
and multimedia PCs to easily play the same compact discs. This
new format allows both audio and data to be integrated on the
same CD.
CD+ uses a new technology called stamped
multisession, which solves the problem of trying to use a
computer CD-ROM title in an audio player. Because the first
track of a computer CD-ROM contains data and not music, the
audio player attempts to play it and the result is static. If
the volume is turned up, the speakers can be damaged.
The new CD+ format will allow a new type of CD to appear
that contains not only music, but also data such as song
lyrics, biographies, and any other text that is desired.
PhotoCD
First announced back in 1990, but not available until 1992,
CD drives or players that display your own CD-ROM recorded
photographs over your television are now being sold by Kodak.
You merely drop off a roll of film at a participating Kodak
developer; later you take home a PhotoCD and drop it into your
Kodak PhotoCD compatible disc player. But what's a PhotoCD
compatible player?
This is a home A/V (Audio Visual) entertainment system
component that is designed to play your PhotoCDs and your
audio CDs as well. Because virtually all data-ready CD drives
also can interpret audio, it's no mean feat for the Kodak CD
players to play audio discs. The player merely reads off the
first track and determines what type of disc you've fed it.
The real breakthrough is in the drive's capability to
determine whether one, two, or dozens of individual photo
"sessions" are on the data disc.
Remember from the High Sierra format discussion that each
data disc holds a VTOC, or Volume Table of Contents, which
tells the CD reader where--and how--the data is laid out on
disc. CD data has, until this point, been single-session in
its encoding. In other words, when a CD is mastered, all the
data that will ever reside on the disc must be recorded in one
session. The format, or the media, has no provision for
returning later to append more information. The PhotoCD
format--along with the XA and CD-I formats discussed
later--not only allow for multiple sessions, but also allow
multiple sessions to be read back on a fully PhotoCD-capable
CD-ROM drive. However, the drive must be capable of finding
the multiple VTOCs associated with the appended sessions.
And this is where some confusion now reigns. When Kodak
first released the PhotoCD, the company maintained that a
drive must be CD-ROM XA compliant to use PhotoCD. An
explanation of the XA specifications follows in the section
"CD-ROM-XA, or Extended Architecture." As of January 1992,
however, Kodak has tested non-XA drives with new software
drivers and approved them as single-session PhotoCD
compatible. In other words, many of the drives shipping right
now may be perfectly suited to reading PhotoCD discs that
contain a single session of photos. The drive can only
recognize the first session, and ignores any data or
subsequent volume entries made after the initial session.
PC-based CD-ROM drives, if supplied with the proper device
driver and Kodak-based software, can read single-session
PhotoCD images. Kodak is licensing the "viewer" portion of its
software so that it can be incorporated into existing software
packages. Special filters--or decoders--will be added to
desktop publishing, word processing, and PC paint software
that will allow them to import PhotoCD images into their
documents.
Kodak has future plans to incorporate synchronized audio
and text to the existing photo format. For these capabilities,
the drive that reads these advanced discs must be
XA-compatible. In addition, drives must be XA-compatible to
read any disc that has multiple recordings.
PhotoCD Production When you drop off your roll of
film, the Kodak developers produce prints, just as they
normally do. After prints are made, however, the process
goes high-tech. Using high-speed UNIX operating system-based
SUN SparcStations, the prints are scanned into the
SparcStation at a very high resolution using ultra-high
resolution scanners. To give you an idea of the amount of
information each scan carries, one color photograph can take
15-20M of storage. When the image is stored on disc, it is
compressed using Kodak's own custom software. The
compressed, stored images are then encoded onto special
writable CD discs. The finished product is packaged in a
familiar CD case and shipped back to your local developer
for pickup.
Even though these scanned images occupy an enormous
amount of media space, the capacity of CD technology can
easily carry 100 photos, at the highest possible resolution.
Because existing television, and even most home computers,
cannot use these ultra-high resolutions, the typical home or
PC-based PhotoCD can hold hundreds of images. See Table 17.3
for more details. Because most of us rarely have that many
photos developed at the same time, Kodak developed the
system in conjunction with Philips so that multiple sessions
can be recorded on one disc. You can have your Thanksgiving
photos developed and recorded to disc in November, for
example, and then bring the same disc back in late December
to have your other holiday photos added to the remaining
portion of the disc. Keep bringing the disc in until it
fills up.
Table 17.3 PhotoCD Resolutions
Resolution |
Description |
256 linesx384 |
Fine for most conventional TVs |
512x768 |
Good for S-VHS TVs and VGA PCs |
1024x1536 |
Beyond current TV technology |
2048x3072 |
Beyond TV or most PC
capacities |
As of this writing, Kodak PhotoCD discs run fine in single
session mode in many current CD-ROM drives--in Philips CD-I
home entertainment systems as well as the Kodak systems.
For multisession capabilities and the capability to use
audio and text on a PhotoCD for the PC, you must have an
XA-compatible CD-ROM drive.
CD-ROM-XA or Extended
Architecture
CD-ROM XA, or Extended Architecture, is
backwards compatible with the earlier High Sierra or ISO 9660
CD-ROMs. It adds another dimension to the world of CD-ROM
technology.
Interleaving
CD-ROM XA drives employ a technique known as
interleaving. The specification calls for the
capability to encode on disc whether the data directly
following an identification mark is graphics, sound, or text.
Graphics can include standard graphics pictures, animation, or
full-motion video. In addition, these blocks can be
interleaved, or interspersed, with each other. For
example, a frame of video may start a track followed by a
segment of audio, which would accompany the video, followed by
yet another frame of video. The drive picks up the audio and
video sequentially, buffering the information in memory, and
then sending it along to the PC for synchronization.
In short, the data is read off the disc in alternating
pieces, and then synchronized at playback so that the result
is a simultaneous presentation of the data.
Mode 1 and Mode 2, Form 1 and Form 2
To achieve this level of sophistication, the CD format is
broken up so that the data types are layered. Mode 1 is
CD data with error correction. Mode 2 is CD data
without error correction. The Mode 2 track, however, allows
what are called Form 1 and Form 2 tracks to exist one after
the other on the Mode 2 track, thereby allowing the
interleaving. These interleaved tracks may include their own
error correction and can be any type of data. Figure 17.3
shows a visual representation of the breakdowns of Mode and
Form structure.
FIG.
17.3 A diagrammatic view of Mode
and Form format for CD-ROM XA.
For a drive to be truly XA-compatible, the Form 2 data
encoded on the disc as audio must be ADPCM (Adaptive
Differential Pulse Code Modulation) audio--specially
compressed and encoded audio. This requires that the drive or
the SCSI controller have a signal processor chip that can
decompress the audio during the synchronization process.
What all this translates into is that drives currently
available may be partially XA- compliant. They might be
capable of the interleaving of data and reading of multi-
session discs, but may not have the ADPCM audio component on
the disc or its controller.
Presently, the only drives with full XA compliance are
produced by Sony and IBM. The Sony drive incorporates the
ADPCM chip on its drive. The IBM XA drive is for IBM's
proprietary Micro Channel bus and is designed for its high-end
PS/2 Model computers.
Manufacturers may claim that their drives are "XA-ready,"
which means that they are capable of multisession and Mode 1
and Mode 2, Form 1 and Form 2 reading, but they do not
incorporate the ADPCM chip. Software developers, including
Kodak, have yet to produce many XA software titles. IBM has a
few under its Multimedia program, but others have not yet hit
the market.
If you get a drive that is fully mode and form compatible
and is capable of reading multiple sessions, you may have the
best available at this time. XA is a specification waiting for
acceptance right now. Audio and video interleaving is possible
without full XA compliance, as MPC (Multimedia PC)
applications under Microsoft Windows demonstrate.
CD-R
Sometimes known as CD-WORM and CD-WO, CD-R
(CD-Recordable) enables you to write your own CDs.
As with mastering any CD, your data must be laid out or
formatted before recording it to the CD-R unit. Often this
layout is performed on a PC with large hard disks or other
magnetic and removable media.
The CD-R is not quite the CD you might expect, however.
Instead of the recording beam burning pits into a metallic or
glass strata, the CD-R media is coated with a dye that has the
same reflective properties as a "virgin" CD --in other words,
a CD reader would see an unrecorded CD-R disc as one long
land. When the recording laser begins to burn data into the
CD-R media, it heats the gold layer and the dye layer beneath.
The result of heating these areas causes the dye and gold
areas to diffuse light in exactly the same way that a pit
would on a glass master disc or a mass-produced CD. The reader
is fooled into thinking a pit exists; but there is no actual
pit, just a spot of less-reflective disc caused by the
chemical reaction of heating the dye and gold.
Many of the newer recordable CD-ROM drives support all the
formats discussed--ISO 9660 all the way through CD-ROM XA. In
addition, these drives read the formats as well, serving as a
ROM reader. Prices have been falling steadily, and are now in
the $700 area for a drive, and under $5 for the blank media.
These drives are now affordable for small businesses, who can
distribute databases easily on CD-ROM discs. After you make a
master, it can cost less than $1 per disc to have duplicates
made, bringing the price of distributing your data to a very
reasonable figure.
CD-E
Although CD-R is a write once standard, it is now possible
to purchase fully re-recordable CD drives. Philips Electronics
and Ricoh have introduced erasable CD-ROMs (called CD-E). The
CD-E standard has been developed and supported by more than 10
manufacturers, including IBM, Hewlett-Packard, Mitsubishi,
Mitsumi, Matsushita, Sony, 3M, Olympus, Philips, and
Ricoh.
The new medium has an archival life of more than 10 years,
or roughly 10,000 access cycles, and will allow at least 1,000
overwrites to occur. As such it is not intended to replace
magnetic media for primary online storage, but can supplement
it for archival purposes. The media has a lower optical
reflectability than standard CDs, requiring an increase of
five times the read/write gain for the drive units.
This new technology is backward compatible with standard
CD-ROM and CD-R technology, meaning that CD-E drives would
read existing CD and CD-R discs. These new drives will
initially be expensive, but if the price falls it may catch on
as a viable backup and online storage solution.
DVD (Digital Versatile Disc)
The future of CD-ROM is called DVD (Digital Versatile
Disc). This is a new standard that dramatically increases the
storage capacity of, and therefore the useful applications
for, CD-ROMs. The problem with current CD-ROM technology is
that it is severely limited in storage capacity. A CD-ROM can
only hold a maximum of about 680M of data, which may sound
like a lot, but is simply not enough for many up and coming
applications, especially where the use of video is
concerned.
One of the primary applications envisioned for the new DVD
standard is a replacement for video tapes. In the future,
instead of renting a tape at your local video store, you will
be able to rent or purchase a movie on a CD-ROM disc! As such,
DVD will have applications not only in computers, but in the
consumer entertainment market as well.
DVD had a somewhat confusing beginning. During 1995, two
competing standards for high capacity CD-ROM drives emerged to
compete with each other for future market share. A standard
called Multimedia CD was introduced and backed by Sony and
Philips Electronics, while a competing standard called the
Super Density (SD) disk was introduced and backed by Toshiba,
Time Warner, and several other companies. If both of these
standards had hit the market as is, consumers as well as
entertainment and software producers would have been in a
quandary over which one to choose!
Fearing a repeat of the Beta/VHS situation, several
organizations including the Hollywood Video Disc Advisory
Group and the Computer Industry Technical Working Group banded
together. They insisted on a single format and refused to
endorse either competing proposal. With this incentive, both
groups worked out an agreement on a single, new, high capacity
CD-ROM in September of 1995. The new standard, called DVD
(Digital Versatile Disc), combines elements of both previously
proposed standards. The single DVD standard has avoided a
confusing replay of the VHS/Betamax fiasco and has given the
software, hardware, and movie industries a single unified
standard to support.
DVD offers an initial storage capacity of 4.7G of digital
information on a single-sided, single-layer disc the same
diameter and half the thickness (0.6mm) of a current CD-ROM.
With MPEG-2 (Motion Picture Experts Group) compression, that's
enough to contain 135 minutes of video, enough for a
full-length, full-screen, full-motion feature film--including
three channels of CD-quality audio and four channels of
subtitles. The initial capacity is no coincidence; the
creation of DVD was driven by the film industry, which has
long sought a storage medium cheaper and more durable than
videotape.
Future plans for DVD include 9.4G double-layer discs as
well as double-sided, double-layer discs that will store 18.8G
(nearly 30 times the capacity of today's CD-ROMs). With
advancements coming in blue light lasers, this capacity may be
increased several fold in the future. DVD drives are also very
fast compared to current CD-ROM technology. The standard
transfer rate is 1.3M/sec, which is approximately equivalent
to a 9X CD-ROM drive.
DVD drives will be fully backward compatible, and as such
will be able to play today's CD-ROMs as well as audio CDs.
When playing existing CDs, the performance will be equivalent
to a standard 4x CD-ROM drive. As such, users who currently
own 4x CD-ROM drives should probably consider waiting for DVD
drives instead of upgrading to a 6x or faster drive. Any
products that require faster than 4x speeds will likely come
out in DVD form and not use current CD-ROM technology
anyway.
If you want to take advantage of DVD's multimedia
capabilities you will need a sound-and-video card that can
handle MPEG-2 and the three DVD audio formats. This type of
hardware is expected to be available along with the drives.
Multimedia CD-ROM
Multimedia is not a specific standard but a descriptive
term. Any CD that incorporates text with graphics, sound, or
video is by definition multimedia. Multimedia CDs exist for
DOS, Macintosh System 7, Windows, OS/2, and UNIX operating
systems and can be in many different formats.
A consortium of hardware and software manufacturers led by
Microsoft Corporation announced the formation of the
Multimedia PC Marketing Council at COMDEX in the fall of 1991.
This council described the recommended platform for
implementing multimedia on PC systems, and as more
manufacturers joined the council, applications and hardware
conformed to the prescribed specifications.
The MPC Council recommends minimum performance requirements
for MPC- compatible CD-ROM drives, however. They are as
follows:
Specification |
MPC Level 1 |
MPC Level 2 |
MPC Level 3 |
Transfer Rate |
Single-Speed (1x) |
Double-Speed (2x) |
Quad-Speed (4x) |
Average Access |
1,000 ms |
400 ms |
200 ms |
The minimum recommended specifications today are the MPC
Level 3 standard. In other words, your drive should meet or
exceed those performance standards.
Far from being an exact specification or format for data,
MPC CD-ROM is a convention for storing audio, animation,
video, and text for synchronization under the Microsoft
Windows operating system from data received from an
MPC-compliant CD-ROM. Microsoft has developed Windows
Application Programmer's Interface software, which allows
CD-ROM software manufacturers to organize the data on their
CDs in such a way that information can be passed to Windows
for processing.
Note that discs labeled as MPC only run under Microsoft
Windows 3.0 or higher with the Microsoft Multimedia
Extensions, or under OS/2 with MMPM. If a drive meets the
minimum MPC Council recommendation for performance, it will
run MPC CD-ROMs under Windows.
Audio drives deliver sound at a preset transfer rate to the
amplifiers. Today's CD-ROM drives can spin at faster rates
when retrieving data. The minimum recommended speed today
would be the Quad-speed drive. Particular applications, such
as live-motion video, especially benefit from this technology.
Data is delivered in a constant stream, allowing the PC to
process the video frames at a smoother rate. Some drives
without high-speed technology, especially those that have no
buffering capabilities, deliver video in a jerky and uneven
manner.
Installing Your Drive
You decided on the drive you want. You ordered it. Now it
has arrived at your doorstep. What next?
Installation of a CD-ROM drive is as difficult or as easy
as you make it. If you plan ahead, the installation should go
smoothly.
This section walks you through the installation of typical
internal (applies to SCSI and IDE) and external (applies to
IDE only) CD-ROM drives with tips that often aren't included
in your manufacturer's installation manuals. Even after you
install the hardware, it isn't always enough to just turn on
the drive and toss in a CD (unless your drive is supported by
Windows 95). Special software must be loaded onto your PC
first.
Avoiding Conflict: Get Your Cards in
Order
Regardless of your type of installation--internal or
external drive--you need to check your CD-ROM drive's
controller before installation. In most cases, you will be
adding your CD-ROM drive to an existing IDE or SCSI
controller. If that is so, the controller will have already
been set up so as not to conflict with other devices in your
system. All you need to do is add the CD-ROM to the chain. If
not, then you will need to configure your new controller's:
- IRQ
- DMA channel
- I/O port address
Refer to Chapter 15, "Hard Disk Interfaces," for help with
your particular IDE or SCSI controller.
Drive Configuration
Configuration of your new CD disk is paramount to its
proper function. Examine your new drive (see Figure 17.4) and
locate any jumpers. For an IDE drive, here are the typical
ways to jumper the drive:
- As the primary (master) drive on the secondary IDE
connection
- As the secondary (slave) drive to a current hard disk
drive
FIG.
17.4 The rear connection
interfaces of a typical IDE internal CD-ROM drive.
If the CD drive is to be the only one on your
secondary EIDE interface, the factory settings are usually
correct (see Figure 17.5). In this case, the jumper is not
being used.
When you use the CD-ROM as a secondary drive--that is, the
second drive on the same ribbon cable--make sure it is
jumpered as the slave drive, and set the hard disk so that it
is the master drive. In most cases, the CD-ROM will show up as
the next logical drive, or D: drive.
FIG.
17.5 An embedded EIDE interface
with a primary and secondary IDE connection.
SCSI drives are a bit easier to jumper because you need
only to select the proper device ID for the drive. By
convention, the boot disk (the C: drive) in a SCSI system is
set as ID0, and the host adapter has the ID of 7. You are free
to choose any other available ID. If your new SCSI drive falls
at the end of a SCSI bus, you will also need to terminate the
drive.
NOTE: IDE/EIDE disks and SCSI CD drives can
co-exist in the same system. The CD drive will need its own
controller or host adapter. Some sound cards have a SCSI
interface built-in.
External (SCSI) CD-ROM Hook-Up
Unpack the CD-ROM carefully. With the purchase of an
external drive, you should receive the following items:
- CD-ROM drive
- SCSI adapter cable
- SCSI adapter card (optional)
This is the bare minimum to get the drive up and running.
You'll probably also find a CD caddy, a manual or pamphlet for
the adapter card, and possibly a sampling of CDs to get you
started.
Take a look at your work area and the SCSI cable that came
with the drive. Where will the drive find a new home? You're
limited by the length of the cable. Find a spot for the drive,
and insert the power cable into the back of the unit. Make
sure that you have an outlet, or preferably a free socket in a
surge-suppressing power strip to plug in the new drive.
Plug one end of the supplied cable into the connector
socket of the drive, and one into the SCSI connector on the
adapter card. Most external drives have two connectors on the
back--either connector can be hooked to the PC (see Figure
17.6). The following sections discuss the extra connector.
Secure the cable with the guide hooks on both the drive and
adapter connector, if provided. Some SCSI cables supplied with
Future Domain 16-bit controllers have a micro-connector for
the adapter end, and simply clip into place.
FIG.
17.6 Older Centronics-style
External CD-ROM drive SCSI connectors.
Finally, your external CD-ROM drive should have a SCSI ID
select switch on the back. This switch sets the identification
number for the drive when hooked to the host adapter. The
adapter, by most manufacturer's defaults, should be set for
SCSI ID 7. Make sure that you set the SCSI ID for the CD-ROM
drive to any other number--6, 5, or 4, for example. The only
rule to follow is to make sure that you do not set the drive
for an ID that is already occupied--by either the card or any
other SCSI peripheral on the chain.
Internal Drive Installation
Unpack your internal drive kit. You should have the
following pieces:
- The drive
- Power cord
- SCSI interface board (optional)
- Internal IDE/SCSI ribbon cable
- Internal CD-Audio cable
- Floppy disks/CD-ROM with device driver software and
manual
- Drive rails and/or mounting screws
Your manufacturer also may have provided a power cable
splitter--a bundle of wires with plastic connectors on
each of three ends. A disc caddy and owner's manual may also
be included.
Make sure that the PC is off and leave the cover off the PC
for now. Before installing the card into the PC bus, however,
connect the SCSI ribbon cable onto the adapter card (see
Figure 17.7).
FIG.
17.7 Connecting a ribbon cable to
a SCSI adapter.
Ribbon Cable and Card Edge
Connector
The ribbon cable should be identical on both ends. You'll
find a red stripe of dotted line down one side of the
outermost edge of the cable. This stripe indicates a pin-1
designation, and ensures that the SCSI cable is connected
properly into the card and into the drive. If you're lucky,
the manufacturer supplied a cable with notches or keys along
one edge of the connector. With such a key, you can insert the
cable into the card and drive in only one way. Unkeyed cables
must be hooked up according to the pin-1 designation.
Along one edge of your SCSI adapter, you'll find a double
row of 50 brass-colored pins. This is the card edge connector.
In small print along the base of this row of pins you should
find at least two numbers next to the pins--1 and 50. Aligning
the ribbon cable's marked edge over pin 1, carefully and
evenly insert the ribbon cable connector. Now insert the
adapter card, leaving the drive end of the cable loose for the
time being.
Choose a slot in the front bay for your internal drive.
Make sure that it's easily accessible and not blocked by other
items on your desk. You'll be inserting the CDs here, and
you'll need the elbow room.
Remove the drive bay cover. Inside the drive bay you should
find a metal enclosure with screw holes for mounting the
drive. If the drive has mounting holes along its side and fits
snugly into the enclosure, you won't need mounting rails. If
it's a loose fit, however, mount the rails along the sides of
the drive with the rail screws, and then slide the drive into
the bay. Secure the drive into the bay with four screws--two
on each side. If the rails or drive don't line up evenly with
four mounting holes, make sure that you use at least two--one
mounting screw on each side. Because you'll be inserting and
ejecting many CDs over the years, mounting the drive securely
is a must.
Once again, find the striped side of the ribbon cable and
align it with pin 1 on the drive's edge connector. Either a
diagram in your owner's manual or designation on the connector
itself tells you which is pin 1.
The back of the CD drive has a power connector outlet.
Inside the case of your PC, at the back of your floppy or hard
disk, are power cords--bundled red and yellow wires with
plastic connectors on them. You may already have an open power
connector laying open in the case. Take the open connector and
plug it into the back of the power socket on the CD-ROM drive.
These connectors only go in one way. If you do not have an
open connector, use the splitter (see Figure 17.8). Disconnect
a floppy drive power cord. Attach the splitter to the detached
power cord. Plug one of the free ends into the floppy drive,
the other into the CD-ROM drive.
FIG.
17.8 Power cord splitter and
connector.
NOTE: It's best to "borrow" juice from the
floppy drive connector in this way. Your hard drive may
require more power or be more sensitive to sharing this line
than the floppy is. If you have no choice--the splitter and
ribbon cable won't reach, for example--you can split off any
power cord that hasn't already been split. Check the power
cable to ensure that you have a line not already overloaded
with a split.
Do not replace the PC cover yet--you need to make
sure that everything is running perfectly before you seal the
case. You're now ready to turn on the computer. For the drive
to work, however, you need to install the software drivers.
SCSI Chains: Internal, External, a
Little of Both
Remember, one of the primary reasons for using a SCSI
controller for your CD-ROM drive is the capability to chain a
string of peripherals from one adapter card, thus saving card
slots inside the PC, and limiting the nightmare of tracking
IRQs, DMAs, and I/O memory addresses.
You can add scanners, tape backup units, and other SCSI
peripherals to this chain (see Figure 17.9). You must keep a
few things in mind, chief among them is SCSI termination.
FIG.
17.9 A SCSI chain of devices on
one adapter card.
Example One: All External SCSI Devices
Say that you installed your CD-ROM drive and added a tape
device to the chain with the extra connector on the back of
the CD-ROM drive. The first device in this SCSI chain is the
adapter card itself. Most modern host adapters are auto
terminating, meaning they will terminate themselves
without your intervention if they are at the end of the SCSI
chain.
From the card, you ran an external cable to the CD-ROM
drive, and from the CD-ROM drive, you added another cable to
the back of the tape unit. The tape unit must then be
terminated as well. Most external units are terminated with a
SCSI cap--a small connector that plugs into the unused
external SCSI connector. These external drive connectors come
in two varieties: a SCSI cap and a pass-through terminator.
The cap is just that; it plugs over the open connector and
covers it. The pass-through terminator, however, plugs into
the connector and has an open end that you can use to plug the
SCSI cable into. This type of connector is essential if your
external drive has only one SCSI connector; you can plug the
drive in and make sure that it's terminated--all with one
connector.
Example Two: Internal Chain and Termination
The same rules apply--all the internal devices must have
unique SCSI ID numbers, and the first and last devices must be
terminated. In the case of internal devices, however, you must
check for termination. Internal devices have terminator packs
or resistors similar to the ones installed on your adapter
card. If you install a tape unit as the last device on the
chain, it must have resistors on its circuit board. If you
place your CD-ROM drive in the middle of this chain, its
resistors must be removed. The adapter card, at the end of the
chain, keeps its resistors intact.
NOTE: Most internal SCSI devices ship with
terminating resistors and/or DIP switches on board. Check
your user's manuals for their locations. Any given device
may have one, two, or even three such resistors.
Example Three: Internal and External SCSI
Devices
If you mix and match external as well as internal devices,
follow the rules. The example shown in Figure 17.10 has an
internal CD-ROM drive, terminated and set for SCSI ID 6; the
external tape unit also is terminated, and we assign it SCSI
ID 5. The SCSI adapter itself is set for ID 7 and, most
importantly, its terminating resistor packs have been
removed.
FIG.
17.10 Examples of various SCSI
termination scenarios.
NOTE: As with any adapter card, be careful
when handling the card itself. Make sure that you ground
yourself first. Chip pullers--specially made tweezers found
in most computer tool kits--are especially useful in
removing resistor packs from adapter cards and internal
peripherals such as CD-ROM drives. The resistor packs have
very thin teeth that are easily bent. Once bent, they're
tough to straighten out and reinsert, so be careful when
removing the packs.
CD-ROM Software on Your PC
After you configure the controller card, you're ready for
the last step--installation of the CD-ROM software. The CD-ROM
needs the following three software components for it to
operate on a PC:
- A SCSI adapter driver (not needed for ATAPI IDE CD-ROM
drives). Most popular SCSI adapter drivers are built-in to
Windows 95.
- A SCSI driver for the specific CD-ROM drive you've
installed. An ASPI driver is built into Windows 95, as is an
ATAPI IDE CD-ROM driver.
- MSCDEX--Microsoft CD Extensions for DOS, which is built
into Windows 95 as the CDFS VxD.
If you are still using DOS, you can have the first two
drivers--the SCSI adapter driver and CD-ROM driver--load into
your system at startup by placing command lines in your
CONFIG.SYS file. The MSCDEX, or DOS extension, is an
executable file added into your system through your
AUTOEXEC.BAT file. This is not required in Windows 95 (unless
you plan to run DOS games); it will auto-detect the drive upon
startup and prompt you to install the correct drivers if it
can't find them in its standard arsenal of device drivers.
Using Windows 95 along with a CD-ROM drive that conforms to
the ATAPI (AT Attachment Packet Interface) IDE specification
does not require you to do anything. All the driver support
for these drives is built into Windows 95, including the ATAPI
driver and the CDFS VxD driver.
If you are running a SCSI CD-ROM drive under Windows 95,
you will still need the ASPI (Advanced SCSI Programming
Interface) driver that goes with your drive. The ASPI driver
for your drive normally will come from the drive manufacturer
and is included with the drive in most cases. Windows 95
includes the corresponding ASPI driver for most SCSI host
adapters, and also automatically runs the CDFS VxD virtual
device driver.
DOS SCSI Adapter Driver
Each SCSI adapter model has a specific driver that allows
communications between the PC and the SCSI interface.
Normally, these drivers conform to the ASPI (Advanced SCSI
Programming Interface). The ASPI driver that goes with the
drive will connect with the ASPI driver that goes with the
SCSI host adapter and allow the adapter and drive to
communicate. An ASPI driver should have been provided with
your SCSI drive and adapter kit. Documentation should also
have been included that walks you through the installation of
the software. You can manually add the SCSI device driver to
your CONFIG.SYS file as follows:
At the front of the CONFIG.SYS file, add the name and path
of the driver with the DEVICE= command: DEVICE=C:\DRIVERS\MYSCSI.SYS
C:\DRIVERS is the subdirectory in which
you copied the SCSI ASPI device drivers. Some drivers have
option switches or added commands that, for example, enable
you to view the progress of the driver being
loaded.
DOS CD-ROM Device
Driver
This driver, as well, should be a part
of your basic installation kit. If not, contact the drive's
manufacturer for the proper device driver for your SCSI
card.
The device driver should come with an
installation program that prompts you for the memory I/O
address for the SCSI adapter on which you installed your
CD-ROM drive. This device driver allows communication with the
drive through the SCSI bus to your PC. Installation programs
add a line similar to the following to your CONFIG.SYS
file: DEVICE=C:\DRIVERS\MYCDROM.SYS /D:mscd001
C:\DRIVERS is the subdirectory that
contains the driver MYCDROM.SYS, the CD-ROM driver for your
specific CD-ROM drive.
Note the /D:mscd001 option
after the preceding statement. This designates this CD-ROM
driver as controlling the first (001), and only, CD-ROM drive
on the system. This portion of the device driver statement is
for the Microsoft DOS Extension driver, which designates
CD-ROM drives in this fashion.
MSCDEX: Adding CDs to
DOS
The Microsoft CD Extensions for DOS
enable the DOS operating system to identify and use data from
CD-ROMs attached to the system. The original DOS operating
system had no provisions for this technology, so "hooks" or
handling of this unique media are not a part of the basic
operating environment. Using these extensions is convenient
for all involved, however. As CD-ROM technology changes, the
MSCDEX can be changed, independently of the DOS system. For
example, most PhotoCD, multiple-session CD-ROM drives require
MSCDEX.EXE version 2.21, which has been modified from earlier
versions to accommodate the newer CD format.
MSCDEX.EXE should be in your software
kit with your drive. If not, you can obtain the latest copy
from Microsoft directly. The latest version of the DOS
extension also is available on CompuServe in the Microsoft
forum. If you are a registered user of the DOS operating
system, the MSCDEX is free. Read the licensing agreement that
appears on the disk or in your manual concerning the proper
licensing of your MSCDEX files.
Your installation software should add a
line similar to the following to your AUTOEXEC.BAT
file: C:\WINDOWS\COMMAND\MSCDEX.EXE /d:mscd001
C:\WINDOWS\COMMAND is the directory in
which the MSCDEX.EXE file is located by default. The
/d:mscd001 portion of the command line tells the
MSCDEX extension the DOS name of the device defined in the
CD-ROM device driver of your CONFIG.SYS file.
NOTE: The MSCDEX and CD-ROM
device driver names must match. The defaults that most
installations provide are used in this example. As long as
the two names are the same, the drivers can find one
another.
Sounds complicated? Don't worry. As
long as you have these three drivers--the SCSI adapter driver,
the CD-ROM driver, and the DOS CD extensions--loaded properly
in your system, the CD-ROM drive will operate as transparently
as any other drive in your system.
Table 17.5 lists the options MSCDEX.EXE
has that you can add to its command line.
Table 17.5 MSCDEX Command
Line Options
Switch |
Function |
/V |
Called Verbose; lists information about
memory allocation, buffers, drive letter assignments,
and device driver names on your screen at boot up when
this option is added to the command line. |
/L: <letter> |
Designates which DOS drive letter you
will assign the drive. For example, /L:G
assigns the drive letter G: to your CD-ROM drive. Two
conditions apply: first, you must not have another drive
assigned to that letter; and second, your
lastdrive= statement in your CONFIG.SYS file
must be equal to or greater than the drive letter you're
assigning. LASTDRIVE=G would be fine.
LASTDRIVE=F would cause an error if you attempt
to assign the CD-ROM drive to the G: drive through the
/L: switch. |
/M: <buffers> |
Enables you to buffer the data from the
CD-ROM drive. This is useful if you want faster initial
access to the drive's directory. Buffers of 10 to 15 are
more than enough for most uses. Any more is overkill.
Each buffer, however, is equal to 2K of memory. So a
/M:10 buffer argument, for example, would take
20K of memory. Note that this does not significantly
increase the overall performance of the drive, just
DOS's initial access to the drive and the access of
large data blocks when the drive is gulping down
live-motion video, for example. You can't turn a 400ms
drive into a speed demon by adding a 200K buffer. With
no /M: argument added, MSCDEX will add, as a
default, six buffers anyway. That may be fine for most
PCs and CD-ROM drives. |
/E |
Loads the aforementioned buffers into DOS
high memory, freeing up space in the conventional 640K.
Early versions of MSCDEX--anything below version
2.1--does not load into extended memory. You must have
DOS 5.0 for this option to load. |
/K |
Kanji (Japanese) support. |
/S |
Enables you to share your CD-ROM drive on
a peer-to-peer network, such as Windows for
Workgroups. |
Note that Windows 95 uses a built-in
CDFS (CD File System) driver that takes the place of MSCDEX.
It is configured through the Registry in Windows 95.
Software
Loading
As mentioned earlier, your drive should
come with installation software that copies the device driver
files to your hard drive. It should also add the necessary
command lines to your CONFIG.SYS and AUTOEXEC.BAT files or to
the SYSTEM.DAT Registry file for Windows 95. When this is
accomplished, you can reboot your machine and look for signs
that all went smoothly in the software
installation.
Following is a series of sample
portions of your boot up screens to give you an idea of what
messages you'll receive when a given driver is properly loaded
into the system. When you're sure that the software is loaded
correctly, try out the drive by inserting a CD into the disc
caddy and loading it into the CD-ROM drive. Then get a
directory of the disc from the DOS prompt by issuing the
following command: DIR/w G:
This command gives you a directory of
the CD you've inserted if your CD has been assigned the drive
letter G.
You can log in to the CD-ROM drive,
just as you would any DOS drive. The only DOS commands not
possible on a CD-ROM drive are those that write to the drive.
CDs, remember, are media that cannot be overwritten, erased,
or formatted.
If you logged in to the CD-ROM and
received a directory of a sample CD, you're all
set.
Now you can power down the PC
and replace the cover.
CD-ROM in
Microsoft Windows 3.x
When your drive is added to your
system, Windows already knows about it through the device
drivers and DOS. The CD-ROM drive is accessible through File
Manager by double-clicking its file cabinet icon. You see your
CD-ROM drive among the drive icons across the top. Windows
knows that the drive is a CD-ROM drive through the DOS
extensions discussed earlier.
You can set your CD-ROM player to play
audio CDs while you are working in Windows. You need to hook
up your drive to a sound card and speakers, or connect the
CD's audio ports to a stereo first. Go to Window's Control
Panel and select Drivers. If you do not see [MCI] CD
Audio among the files in the driver's list, choose Add.
Insert the Windows installation disk that contains the CDAUDIO
driver. When the driver appears on the list, exit the Drivers
and Control Panel windows.
Double-click the Media Player icon.
Under Devices, select CD. A listing of the track numbers on
your audio CD appears along the bottom edge of the Media
Player. The controls on Media Player are similar to those of
an audio CD player, including track select, continuous play,
and pause (see Figure 17.11).
Many drive manufacturers supply
DOS-based CD audio players with their systems. Check your
installation manual and software disks for these utilities.
CD-ROM in
Windows 95 and Windows NT 4.0
As stated earlier, Windows 95/NT
includes virtually all the drivers you will need to run your
CD-ROM drive, making the software installation automatic.
Windows automatically recognizes most IDE CD-ROM drives, and
with the addition of the appropriate drive-specific ASPI
driver, most SCSI CD-ROM drives as well.
FIG.
17.11 The Media Player with an
audio CD loaded.
There are several new capabilities with
CDs in Windows 95/NT. The most dramatic is the Autoplay
feature. Autoplay is a feature integrated into Windows 95 that
enables you to simply insert a CD into the drive, and Windows
will automatically run it without any user intervention. It
will also detect whether that particular CD has already been
installed on your system, and if not, it will automatically
start the install program. If the disc has already been
installed, it will start the application program on the
disc.
The Autoplay feature is simple. When
you insert a disc, Windows 95 automatically spins it and looks
for a file called AUTORUN.INF. If this file exists, Windows 95
opens it and follows the instructions contained within. As you
can see, this Autoplay feature will only work on new CDs that
have this file. Most software companies are now shipping
CD-ROM titles that incorporate the Autoplay
feature.
Windows 95/NT includes a new version of
the Media Player found in Windows 3.x called the CD-Player.
This application enables you to play audio CDs in your drive
while you work at the computer. The CD-Player features
graphical controls that look like a standard audio CD-ROM
drive, and even has advanced features found in audio drives
such as random play, programmable playback order, and the
capability to save play list programs.
Troubleshooting
CD-ROMs
Some people believe that CD-ROM discs
and drives are indestructible compared to their magnetic
counterparts. Actually, the modern CD-ROM drive is far less
reliable than the modern hard disk! Reliability is the bane of
any removable media, and CD-ROMs are no exception.
By far the most common causes of
problems with CDs or CD-ROM drives are scratches, dirt, or
other contamination. Small scratches or fingerprints on the
bottom of the disc should not affect performance because the
laser focuses on a point inside the actual disk, but dirt or
deep scratches can interfere with reading a disc.
To remedy this type of problem, you can
clean the bottom surface of the CD with a soft cloth, but be
careful not to scratch the surface in the process. The best
technique is to wipe the disc in a radial fashion, using
strokes that start from the center of the disc and emanate
toward the outer edge. This way any scratches will be
perpendicular to the tracks rather than parallel to them,
minimizing the interference they might cause. You can use any
type of solution on the cloth to clean the disc, so long as it
will not damage plastic. Most window cleaners are excellent at
removing fingerprints and other dirt from the disc and will
not damage the plastic surface.
If there are deep scratches, they can
often be buffed or polished out. A commercial plastic cleaner
such as that sold in auto parts stores for cleaning plastic
instrument cluster and tail lamp lenses is very good for
removing these types of scratches. This type of plastic polish
or cleaner has a very mild abrasive that serves to polish
scratches out of a plastic surface. Products labeled as
cleaners are usually designed for more serious scratches,
while those labeled as a polish are usually milder and work
well as a final buff after using the cleaner. Polishes can be
used alone if the surface is not scratched very
deeply.
Read errors can also occur when dust
accumulates on the read lens of your CD-ROM drive. You can try
to clean out the drive and lens with a blast of "canned air,"
or by using a CD drive cleaner (which can be purchased at most
music stores that sell audio CDs).
If your discs and your drive are clean,
but you still can't read a particular CD-ROM, then your
trouble might be due to disc capacity. Early CD-ROM discs had
a capacity of about 550M (equivalent to about 60 minutes of CD
audio). More recently, the capacity of a standard CD has been
pushed to 680M (74 minutes of CD audio). Many older CD-ROM
drives are unreliable when they try to read the outermost
tracks of newer discs where the last bits of data are stored.
You're more likely to run into this problem with a CD that has
lots of data--including some Microsoft multimedia titles such
as Ancient Lands, Art Gallery, and Complete Baseball. If you
have this problem, you may be able to solve it with a firmware
or driver upgrade for your CD-ROM drive, but it's possible
that the only solution will be to replace the
drive.
Sometimes too little data on the disc
can be problematic as well. Some older CD-ROM drives use an
arbitrary point on the disc's surface to calibrate their read
mechanism and if there happens to be no data at that point on
the disc, the drive will have problems calibrating
successfully. For example, some CD-ROM drives are not able to
calibrate successfully with the Microsoft Flight Simulator 5.1
CD-ROM because that disc does not have very much data on it.
Fortunately, this problem can usually be corrected by a
firmware or driver upgrade for your CD-ROM drive.
Many older drives have had problems
working under Windows 95. If you are having problems, contact
your drive manufacturer to see if there is a firmware or
software driver upgrade that may take care of your problem.
With new Eight-speed drives approaching $50 in cost, it may
not make sense to spend any time messing with an older drive
that is having problems. It would be more cost-effective to
simply upgrade to a new 8x or 12x drive instead!
If you are having problems with only
one particular disc, and not the drive in general, then you
may find that your difficulties are in fact caused by a
defective disc. See if you can exchange the disc for another
to determine if that is indeed the cause.
|