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What is Blu Ray Disc

Caring for Optical Media

Short presentation of DVD Capacity (Sides and Layers)

DVD Construction and Technology

DVD Tracks and Sectors

Data Encoding on a CD

DVD Formats and Standards

Compact Disc information and CD Drive Formats

CD ROM File Systems

Installing and Configuring an ATAPI Tape Drive

Installing and Configuring a SCSI Tape Drive

A Brief History of CD

DVD History

Configuring Windows 9X/2000/XP to Support a Tape Drive

CD ROM and CD R tracks and sectors

The nature of the CD ROM medium and operation of CD recorders make the creation and writing of a CD ROM a more complex operation than simply copying files to a hard disk drive. Because CD ROMs are essentially sequentially recorded media, the CD recorder wants to receive data and write it to disc as a continuous stream. In most CD recorders, the stream of data cannot be interrupted once it starts. An interruption in the data flow can result in an error in recording. Moreover, to obtain the highest capacity possible from a given CD, you want to limit the number of sessions into which you divide the disc. As noted above, each session steals at least 13MB from disc capacity for the overhead of the session’s lead-in and lead-out.

If your system cannot supply information to your CD recorder fast enough, the result is a buffer underrun error. When you see such an error message on your screen, it means your CD recorder has exhausted the software buffer and run out of data to write to the disc. You can prevent this error by increasing the size of the buffer if your software allows it. Or you can better prepare your files for transfer to CD. In particular, build a CD image on a hard disk that can be copied on the fly to the CD.

The best strategy is to give over your PC to the CD writing process, unloading any TSR programs, background processes, or additional tasks in a multi-tasking system. Screen savers, popup reminders, and incoming communications (your modem answering the phone for data or a fax) can interrupt your CD session and cause you to waste your time, a session, or an entire disc.

Your system needs to be able to find the files it needs to copy to your CD ROM as efficiently as possible. Copying multiple short files can be a challenge, particularly if your hard disk is older and slower or fragmented. CD recorder makers recommend disks with access times faster than about 19 milliseconds. An AV-style hard disk is preferable because such drives are designed for the smooth, continuous transfer of data and don’t interrupt the flow with housekeeping functions such a thermal calibration. You’ll also want to be sure that your files are not fragmented before transferring them to CD. Run your defrag utility before writing to your CD.

Depending on the manufacturer of your CD recorder and the software accompanying it, you may have a choice of more than one mode for copying data to CD. In general, you have two choices, building a CD image on your hard disk and copying that image intact to your CD. Some manufacturers call this process "writing on the fly." From a hardware standpoint, this is the easiest for your system and CD recorder to cope with because the disk image is already in the form of a single huge file with all of the directory structures needed for the final CD in their proper places. Your system need only read your hard disk and send a steady stream of data to the CD recorder.

The alternative method is to create the CD structure in its final form on the CD itself. Some manufacturers call this "writing a virtual image." In making a CD by this method, your CD recorder’s software must follow a script or database to find which files it should include on the disk and locate the files on your hard disk. The program must allocate the space on your CD, dividing it into sectors and tracks, while at the same time reading the hard disk and transferring the data to the CD.

Media

Discs used in CD recorders differ in two ways from those used by conventional CD players—besides being blank when they leave the factory. CD-R discs require a recordable surface, something that the laser in the CD recorder can alter to write data. This surface takes the form of an extra layer of dye on the CD-R disc. Recordable CDs also have a formatting spiral permanently stamped into each disc.

Dye Layer

As with other CDs, a recordable disc has a protective bottom layer or substrate of clear polycarbonate plastic that gives the disc its strength. A thin reflective layer is plated on the polycarbonate to deflect the CD beam back so that it can be detected by the drive. Between this reflective layer and the normal protective top lacquer layer of the disc, a CD-R disc has a special dye layer. The dye is photoreactive and changes its reflectivity in response to the high power mode of the CD recorder’s laser.

Three compounds are commonly used for photo-reactive dyes used by CD-R discs. These are most readily distinguished by their color: either green, gold, or blue.

Green

Not surprisingly, green CD-R discs look green. The dye layer, based on a cynanine compound, is green and lustrous from the reflective backing partly shining through. Taiyo Yuden developed the photoreactive dye which was used for the first CD-R discs, including those used during the development of the CD-R standards. Even now, green CD-R discs are believed to be more forgiving of variations in laser power during the read and write processes. The green cynanine dye is believed to be permanent enough to give green CD-R discs a useful life of about 75 years. In addition to Taiyo Yuden, several companies including Kodak, Ricoh, TDK and Verbatim make green CD-R discs.

Gold

Kodak made the world aware of gold CD-R discs when it introduced its Photo-CD system, touting them as being higher quality than the green variety. The gold dye, a phthalocyanine, was actually developed by Mitsui Toatsu Chemicals. The chief advantage of gold over green discs is longer life because the dye is less sensitive to bleaching by ambient light. If it were on a dress or shirt, it would be more colorfast. Gold CD-R discs are believed to have a useful life of about 100 years. Some people believe that gold discs are also better for high speed (2x or 4x) recording than are green discs. Mitsui Toatsu and Kodak manufacture most gold CD-R discs. Kodak Photo-CD discs also have an extra coating the company called "Inforguard" which makes them more resistant to scratches (and thus prolongs their life when used in hostile environments like the typical home), but the coating is independent of the dye color.

Blue

The most recent of the CD shades is blue, a color that results from using cynanine with a alloyed silver substrate. The material is proprietary and patented by Verbatim, currently the sole manufacturer. According to some reports, it is more resistant to ultraviolet radiation than either green or gold dyes and makes reliable discs with low block error rates. Verbatim also adds a scratch resistant coating to its discs, but as with PhotoCDs, the coating is independent from the disc color.

Some manufacturers use multiple layers of dyes on their discs, sometimes even using two different dyes. The multiple-layer CD-R discs are often described as green-green, gold-gold, or green-gold depending on the colors of the various layers.

Additionally, the reflective layers of recordable CDs also vary in color. They may be silver or gold, which subtly alters the appearance of the dye.

There should be no functional difference between the different CD-R colors—all appear the same hue to the monochromatic laser of a CD drive that glows at a wavelength of 780 nanometers. But while all of the CD-R materials reliably yield approximately the same degree of detectable optical change, as a practical matter they may act differently. Some early CD ROM readers may have varying sensitivities to the materials used in CD-R discs and will reliably read one color but not another. There is no general rule about which color is better or more suited to any particular hardware. The best strategy is to find what works for you and stick with it.

Physical Format

The polycarbonate substrate of all CD-R discs has a spiral groove physically stamped into it. More than a simple channel, this groove incorporates sector formatting data which incidentally defines the capacity of the disc. Because this format is physically encoded on the disc, it cannot be altered, and you cannot increase the capacity of a CD-R disc (although you can reduce the capacity of the disc simply by not writing to its entire surface). You can think of the groove as being the low level format of the recordable CD.

Capacity

With a read-only medium, you normally don’t have to concern yourself with the issue of storage capacity. That’s for the disc maker to worry about—the publisher has to be sure everything fits. With about 650 megabytes of room on the typical CD and many products requiring only a few megabytes for code, the big problem for publishers is finding enough stuff to put on the disc so that you think you’re getting your money’s worth.

The advent of recordable CDs changes things entirely. With CDs offering convenient long-term storage for important files such as graphic archives, you’ll be sorely tempted to fill your CDs to the brim. You’ll need to plan ahead to make all your files fit.

CD ROMs have substantial overhead that cuts into their available capacity. If you don’t plan for this overhead, you may be surprised when your files don’t fit.

Raw Capacity

CD ROM capacities are measured in minutes, seconds, and sectors, based on the audio format from which engineers derived the medium. Recordable CDs come in four capacities: 18 and 21 minute discs are 80 millimeters in diameter; 63 and 74 minute discs are 120 millimeters in diameter.

Two kinds of file overhead affect the number of bytes available on a given recordable CD that can actually be used for storage. One is familiar from other mass storage devices, resulting from the need to allocate data in fixed-size blocks. The other results from the format structure required by the CD standards. Table below reflects the effects of this overhead in CD-R capacity.

Logical Block Padding

As with most hard and floppy disks, CD ROMs allocate their storage in increments called logical blocks. Although logical block sizes of 512, 1024, and 2048 bytes are possible with today’s CD drives, only the 2048-byte logical block format is in wide use. If a file is smaller than a logical block, it is padded out to fill a logical block. If a file is larger than one logical block, it fills all its logical blocks except the last, which is then padded out to be completely filled. As a result of this allocation method, all files except those that are an exact multiple of the logical block size require more disc space than their actual size. In addition, all directories on a CD require at least one logical block of storage.

That said, CD ROMs are typically more frugal with their storage than today’s large hard disks. The standard DOS and Windows 95 disk formats require allocation units called clusters of 16 kilobytes for disks with capacities between one and two gigabytes, so they waste substantially more space on allocation unit padding than do CDs.

Format Overhead

Because audio CDs require lead-in and lead-out tracks, the Yellow Book standard for CD ROM makes a similar allowance. The specifications require that data on a CD ROM begin after a two-second pause, followed by a lead-in track 6500 sectors long. Consequently, the first two seconds of storage space and the lead-in area on a CD are not usable for data. These two seconds comprise a total of 150 sectors each holding 2048 bytes, which trims the capacity of the disc by 307,200 bytes. The 6500 sector lead-in consumes another 13,312,000 megabytes. The lead-out gap at the end of a storage session and pre-gap that allows for a subsequent session consume another 4650 sectors or 9,523,200 bytes.

The ISO 9660 file structure also eats away at the total disk capacity. The standard reserved the first 16 sectors of the data area—that’s 32,768 bytes—for system use. Various elements of the disc format also swallow up space. The root file, primary volume descriptor, and volume descriptor set terminator each require a minimum of one sector. The path tables require at least two sectors. The required elements consequently take another five sectors or 10,120 bytes of space. Discs with complex file structures may exceed these minima and lose further storage space.

The more sessions you divide a given CD into, the less space will be available for your data. Each session on a multi-session CD requires its own lead-in. Consequently, each session requires at least 13MB of space in addition to the file structure overhead.

Vulnerabilities

No matter the dye used, recordable CD media are not as durable as commercially stamped CDs. They require a greater degree of care. They are photosensitive, so you should not expose them to direct sunlight or other strong light sources. The risk of damage increases with exposure. The label side of recordable CDs is often protected only by a thin lacquer coating. This coating is susceptible to damage from solvents such as acetone (finger nail polish remover) and alcohol. Many felt tip markers use such solvents for their inks, so you should never use them for marking on recordable CDs. The primary culprits are so-called permanent markers, which you can usually identify by the strong aroma of their solvents. Most fine point pen-style markers use aqueous inks, which are generally safe on CD surfaces. Do not use ballpoint, fountain pen, pencil or other sharp-tipped markers on recordable CDs because they may scratch through the lacquer surface and damage the data medium.

The safest means of identifying a recordable CD is using a label specifically made for the recordable CD medium. Using other labels is not recommended because they may contain solvents that will attack the lacquer surface of the CD. Larger labels may also unbalance the disc and make reading it difficult for some CD players. In any case, once you put a label on a recordable CD, do not attempt to remove it. Peeling off the label likely will tear off the protective lacquer and damage the data medium.

Operation

Creating a CD is a complete process. The drive doesn’t just copy down data blocks as your PC pushes them out. Every disc, even every session, requires its own control areas to be written to the disc. Your CD-R drive doesn’t know enough to handle these processes automatically because the disc data structure depends on your data and your intentions. Your CD-R drive cannot fathom either of these. The job falls to the software you use to creates your CD-R discs.

Your CD creation software organizes the data for your disc. As it sends the information to your CD-R drive, it also adds the control information required for making the proper disc format. After you’ve completed writing to your disc, the software fixates the disc so that it can be played. The last job is left to you—labeling the disc so you can identify the one you need from a stack more chaotic than the pot of an all night poker game.

Speed

As with ordinary CD ROM, the speed of CD-R drives is the transfer rate of the drive measured in multiples of the basic audio CD speed, 150KB/sec. The very first CD recorders operated at 1x speed, and each new generation has doubled that speed. The fastest drives currently operate at 4x, although technical innovation can increase that just as it has improved basic CD speed.

Most CD recorders have two speed ratings, one for writing and one for reading. The writing speed is invariably the same or less than the reading speed. Advertisements usually describe drives using two numbers, the writing speed (lower number) first. The most common speed combinations are: 1x1, single-speed read and write; 1x2, single-speed write and double-speed read; 2x2 double-speed writing and reading; 2x4 double-speed writing and quadruple-speed reading; and 4x4 quadruple-speed in both writing and reading.

How fast a CD recorder writes is only one factor in determining how long making one or more CDs will take. Other variables include your system, writing mode (whether you try to put files together for a CD session on the fly or try to write a disc image as one uninterrupted file), and the number of drives.

Your system and writing mode go hand-in-hand. As noted below, a CD recorder requires a constant, uninterrupted stream of data to make a disc. The speed at which your PC can maintain that data flow can constrain the maximum writing speed of a CD-R drive. Factors that determine the rate of data flow include the speed of the source of the data (your hard disk), the fragmentation of the data, and the interfaces between the source disk and your CD recorder.

Most CD recorders have built-in buffers to bridge across temporary slowdowns in the data supply, such as may be involved in your hard disk’s read/write head repeatedly moving from track to track to gather together a highly fragmented file or when an older, non-A/V drive performs a thermal calibration. Even with this bridge action, however, such hard disk slowdowns reduce the net flow of data to the CD recorder. If you try to create a CD by gathering together hundreds of short hard disk files on the fly, your hard disk may not be able to keep up with the data needs of a 4x CD recorder. In fact, if the files are many and small, the hard disk may not even be able to maintain 1x speed, forcing you to resort to making an image file before writing to disc.

Current CD recording software is oriented to SCSI devices. It works optimally with moving files from SCSI-based hard disks and CD readers. When your data originates on an IDE or EIDE hard disk or CD reader, this software slows down, possibly knocking you from 4x to 2x or 1x operation in writing CDs. In fact, some software only allows operations such as copying CD tracks from SCSI CD readers. To work with IDE or EIDE CD tracks, you may first have to build an image file on your hard disk drive. In other words, you should carefully check the requirements of the recording software before you invest in it.

The bottom line is that your present PC may not be able to deliver data at the rate required by a 4x CD recorder. In that a 4x drive is substantially more expensive than a 2x drive, you may be wasting money on speed you cannot use. To take full advantage of a 4x drive with today’s software, you may also have to invest in a Fast SCSI drive or even an Ultra SCSI hard disk drive and a bus mastering host adapter to serve as the data source.

When you have to produce a large number of CDs quickly, one of the best strategies is to use multiple drives. Five drives writing simultaneously cuts the net creation time of an individual CD by 80 percent. For moderate volume applications, stacks of CD writers can make a lot of sense—and CDs. For large volume applications (generally more than a few hundred), pressing CDs is the most cost effective means of duplication, albeit one that requires waiting a few days for mastering and pressing.

Disc Writing Modes

Depending on your CD-R drive and your CD creation software, you may have your choice of the mode you use for writing to your CD. The mode determines what you can write to your discs and when. Typically, you don’t have to worry about the writing mode because your software takes care of the details of it automatically. However, some drives and software may be limited to the modes under which they can operate.

The basic CD writing modes are four: track-at-once, multi-session, disc-at-once, and incremental writing. Each has its own requirements, limitations, and applications.

Track-at-Once

The most basic writing method for CDs is the creation of a single track. A track can be in any format that your CD-R drive can write, for example, a CD ROM compatible disc or a CD-DA disc for your stereo system. The track-at-once process writes an entire track in a single operation. A track must be larger than 300 blocks and smaller than the total capacity of the disc minus its overhead.

Writing track-at-once requires only that you designate what files you want to put on a CD. Your CD creation software takes over and handles the entire writing process.

Originally the big limitation of track-at-once writing was that you could write only one track on a disc in a single session. Consequently, unless you had a lot to write to your disc already prepared beforehand, this process was wasteful of disc space. Some modern CD systems can add one track at a time to a disc within a single session, even allowing you to remove the disc from the drive and try it in another in the middle of the process.

Each track has overhead totaling 150 blocks for run-in, run-out, pre-gap and linking. CD standards allow 99 tracks per disc; consequently, if your tracks are small you may waste substantial capacity. Writing the maximum number of blocks of minimal size (300 blocks plus 150 block of overhead each) will only about half fill the smallest, 18-minute CD disc (44,550 blocks on a 81,000 block disc).

Track Multi-Session

Sometimes called track incremental mode, track multi-session mode is the most common means of allowing you to take advantage of the full capacity of CDs. Track multi-session writing allows you to add to CDs as you have the need by dividing the capacity of the disc into multiple sessions, up to about 50 of them. Each session has many of the characteristics of a complete CD including its own lead-in and lead-out areas as well as table of contents.

In fact, the need for these special formatting areas for each session is what limits the number of sessions on the disc. The lead-in and lead-out areas together require about 13.5 megabytes of disc space. Consequently, CDs with a total capacity of 680 megabytes can hold no more than about 50 sessions.

When the CD standards were first created, engineers didn’t even consider the possibility that individual consumers would ever be able to write their own discs. They assumed that all discs would be factory mastered in a single session. They designed early CD drives to recognize only one session on a disc. Many older CD ROM drives (particularly those with 1x and 2x speed ratings) were single-session models and cannot handle multi-session discs written in track multi-session mode. Single-session drives generally read only the first session on a disc and ignore the rest.

Another problem that may arise with multi-session discs is the mixing of formats. Many CD players are incapable of handling discs on which CD ROM Mode 1 or 2 sessions are mixed with XA sessions. The dangerous aspect of this problem is that some CD mastering software (and CD drives) allow you to freely mix formats in different sessions. You may create a disc that works when you read it on your CD drive that cannot function in other CD drives. The moral is not to mix formats on a disc. (Don’t confuse format with data type. You can freely mix audio, video, and pure data as long as they are written in the same format, providing the one you choose is compatible with all three data types.)

Most modern CD-R machines allow you to write more than one track in a given session. The advantage of this technique is the elimination of most of the 13.5MB session overhead. Instead of lead-in and lead-out tracks, each pair of tracks is separated by 150 blocks (two seconds) of pre-gap—overhead of only about 300K. The entire session must, of course, be framed by its own lead-in, table of contents, and lead-out areas.

In multi-session discs, the drive writes to the lead-in area after it finishes with the data on the disc. The lead-in contains the table of contents for the session as well as an indication of the remaining writable area on the disc. The lead-in of the last session on the disc indicates that no more sessions are present, closing the disc.

Disc-at-Once

Old-fashioned vinyl phonograph records were cut as a single, continuous process. From the moment the cutting stylus plunked down on the master disk until the disk finished spinning around in the capture track, the mastering process had to be free of interruptions. After all, any gap in the spiral track of the phonograph record would stall your record player. To cut a master record, the engineers prepared a master tape that was complete in every detail of everything that was to go on the final disk, including blank tape for the gaps between cuts on the final disk.

The CD equivalent to making such a master disk is the disc-at-once process. As with cutting a master record, the disk-at-once process must be completely free from interruption from the beginning of the lead-in area to the completion of the lead-out area. The table of contents, all tracks, and the Q channel must all be prepared before the writing process begins. The entire disc will be written in one swoop in the order that the formatting data appear on the disc (for example, the lead-in will be written before the data). Typically, to make a CD using disc-at-once writing, you’ll prepare an exact image of the CD and store it on a hard disk. The hard disk must be A/V rated so that it does not interrupt the data stream for thermal calibration or other housekeeping and thus cause buffer underrun (see the following "Underrun" section).

In effect, disc-at-once is a combination of track-at-once and multi-session writing that simply extends across the entire CD (or as much of it as will ever be used).

Disc-at-once is the recording method that must be used when you prepare a disc to serve as master for making mass produced CDs. Because the laser never turns off, a disc recorded using the disc-at-once mode contains no link blocks.

Incremental Writing

If you could make a CD-R work like a conventional hard disk, it would be capable of incremental writing. That is, you could add data to your disc whenever you needed to simply by saving a file. To do this, your CD drive has to modify its file system to reflect the additional data. Although it is possible to design a CD file system that allows this kind of writing, the ISO 9660 standard did not foresee such a possibility. It requires that all the file information be written in the table of contents when you create a session. Multi-session discs sidestep this problem by creating a new file system every time you write a new session—with all the overhead of a complete file system—whoops, there goes another 13.5 megabytes.

CD makers have developed a new file standard that allows incremental writing of new data one file at a time without the multi-session overhead. The initial effort at such a file system was developed as ECMA 168. A later standard, ISO 13346 was based upon it, and covered the disk and file structure of write-once and rewritable media that use non-sequential recording for information interchange. Because the ISO standard was designed to be all-embracing, the Optical Storage Technology developed a subset of it aimed specifically at DVD and CD-R media. Called the Universal Disk Format), the CD-R version combines the UDF format with ISO 9660 to support incremental writing.

Because it extends ISO 9660, older CD drives may not be capable of reading discs written using the new standard. They may require new drivers to recognize the altered file structure.

Underrun

No matter the mode, the CD writing process is continuous start to finish. The laser switches on at the beginning of a session and remains in continuous operation until that session is finished. The CD format requires the interleaving of data between blocks during the writing process to help ensure data integrity. To properly interleave the data, the drive needs an overview of the data. To gain this overview, the drive has a data buffer from which it draws the data to write.

For the laser in a CD-R drive to operate continuously, it must have a continuous supply of data to keep its buffer filled with enough information to properly perform the interleaving. If at any time it runs out of data to write, the writing process is interrupted. Unlike hard disks, the CD drive can’t pick up where it left off on the next spin of the disc. The error resulting from the interruption of the data flow is termed buffer underrun.

CD players see the interrupted session as an error (which it is) that may render the disc unplayable. In other words, buffer underrun ruins a disc. Better CD-R drives allow you to close the interrupted session and recover the remaining space on the disc for other sessions.

Testing

To prevent your wasting discs with inadvertent data underruns, most CD-R mastering software makes a trial run or test of the recording session before actually committing your data to disc. The test involves performing exactly the same steps as the actual write operation—including operating the laser in the drive in its write mode—but keeps the power of the laser at read level. The CD-R drive runs through the entire write operation but the lower power of the laser prevents it from affecting (and potentially ruining) a disc.

If the recording software discovers a problem during recording that would cause an underrun or other problem, it advises you how to sidestep the problem, typically by stepping down to a lower writing speed on your CD-R drive or, as a last resort, defragmenting your hard disk.

The only problem with pre-write testing is that the trial run takes as long as writing everything to your disc, essentially doubling the write time of every disc you make. Most CD mastering programs allow you to switch off this pre-write testing. Although you do this at your own peril (and the expense of ruined CDs), if you’re making a batch of discs it is a viable time saving option. In general, if you can write the first disc successfully, you can run through dozens of additional copies without worry.

Fixation

Before a CD that you write can be read by a CD ROM drive or the audio CD player in your stereo system, it must be have an overall table of content that follows the ISO 9660 standard. The process of finishing the disc for reading is termed fixation. In the process of fixation, the disc is finalized when your CD-R drive writes an overall absolute lead-in area and absolute lead-out area for the entire disc.

Multi-session drives also can create discs which are fixated for appending. The individual sessions each have their own table of contents that reflects the sessions actually written on the disc, but the disc lacks the overall lead-in and lead-out areas. When you’ve added the last session to the disc, the finalization process writes an indication on the disc that no further sessions are present, then writes the overall disc lead-in and lead-out areas, completing a table of contents compatible with the ISO 9660 standard. Most CD mastering programs refer to this finalization process as closing the disc.

Software that performs packet writing—for example, Sony’s CDRFS (Compact Disc Recordable File System)—may require a process termed freezing the disc before you can use packet-written discs in ordinary CD players. The freezing process writes lead-in and lead-out areas on the disc. After a disc has been frozen, you can still write additional sessions onto it, providing, of course, additional capacity is available. The freeze process only subtracts from the available capacity, draining away the 13MB of overhead required by any single session.

Labeling

The last step in preparing a CD-R disc for use is labeling it so that you can later identify its contents without having to shove it into your CD drive first. You have your choice of several options—each with its own requirements and limitations—for labeling your CDs.

The easiest way to label a CD is to just scribble on its back surface, the one that has the manufacturer’s logo and other information already printed on it. You can directly write anywhere on this side of the disc. However, to prevent damage to the disc, damage that won’t be immediately apparent but may gradually cause the disc to deteriorate, you should only use a permanent marker that uses water soluble ink. Markers with the traditional "Magic Marker" smell have volatile solvents that can leech through the protective coating on your CDs and affect the data storage layers. Never use ballpoint pen, pencil, or any sharp instrument to label discs. Nor should you use the traditional alternative to sharp objects, crayons, because they leave residue that may flake off into the drive mechanism when the disc plays. Moreover, discs get hot inside the drive, which can melt the crayon wax, allowing it to gum up the works.

Labels will give your discs a more professional look because you can take advantage of the full facilities of your computer printer to render high quality text and multi-color artwork. Again, the chemicals in the adhesives of some labels can have long-term deleterious effects on the CD medium. Choose only label specifically designed for CDs.

Some people have reported problems with labels in high speed (8x and 10x) CD players. They believe that the labels shift the balance of the disc in the drive, causing it to shake as it spins. Drive manufacturers do not believe that such small differences in balance affect drive performance. However, because of the high speed at which discs spin in some players, surface irregularities, such as wrinkled or folded labels, may create turbulence and unsteadiness in the rapidly spinning discs. Ensure that your labels lie flat against the disc surface and do not overhang the edge of the disc. Don’t try pulling a label from a disc, even one that’s only partially stuck, because you may rip part of the surface of the disc along with the adhesive.

Several manufacturers offer special printers designed specifically for low volume CD writing. Models based on thermal wax technology create on-disc labels that look like they have been silk screened. This technology will work with almost any recordable CD. Other CD-R labeling machines use ink jet technology. These require specially prepared discs that have a specially prepared labeling area to which ink jet ink can adhere.

Typically, you’ll label a disc after you’ve finished writing the last session to it. Some drive makers recommend that you label your discs before you start writing, however. The label may change some performance characteristics (optical or mechanical) of the drive. For example, some CD-R drives have Optimal Power Control circuits that ensure the writing laser is operating at peak efficiency, changing its intensity to match the reflectivity of the disc. If you label the disc before you write to it, the electronics of the drive can often compensate for the changes the label makes. As a result, your discs will be more reliable.