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Upgrading & Repairing PCs Eighth Edition

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# CD-ROM Drives

- What Is a CD-ROM?
  - CD-ROM, a Brief History
  - CD Technology
  - Inside Data CDs
- What Types of Drives Are Available?
  - CD-ROM Drive Specifications
  - Interface
  - Loading Mechanism
  - Other Drive Features
- CD-ROM Disc and Drive Formats
  - Data Standard: ISO 9660
  - High Sierra Format
  - CD-DA (Digital Audio)
  - CD+
  - PhotoCD
  - CD-ROM-XA or Extended Architecture
  - CD-R
  - CD-E
  - DVD (Digital Versatile Disc)
- Multimedia CD-ROM
- Installing Your Drive
  - Avoiding Conflict: Get Your Cards in Order
  - Drive Configuration
  - External (SCSI) CD-ROM Hook-Up
  - Internal Drive Installation
  - Ribbon Cable and Card Edge Connector
  - SCSI Chains: Internal, External, a Little of Both
  - CD-ROM Software on Your PC
- Software Loading
  - CD-ROM in Microsoft Windows 3.x
  - CD-ROM in Windows 95 and Windows NT 4.0
- Troubleshooting CD-ROMs

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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 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.

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