About CD-R and CD-RW
A Glossary of terms covering CD/DVD Recording and Recordable Media
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About CD-R and CD-RW |
| What alternatives are available to copy CDs? |
| There are several different methods available to make one or multiple copies of existing CDs ranging from single CD-R and CD-R/RW recorders to specialized devices that automatically duplicate and label discs and, for large runs, commercial mass replication. Options are distinguished by cost, speed, convenience and capability. When dealing with commercial software and audio discs keep in mind copyright laws and that copy protection systems may be employed to hinder straightforward duplication. |
| Computer CD-R and CD-R/RW Recorders |
| By far the quickest and least expensive way to duplicate a disc is to simply copy it using a computer outfitted with a CD-R or CD-R/RW recorder combined with off the shelf writing software. In addition to creating discs from scratch many basic writing software packages duplicate most standard CD formats. Specialized copying software is also available with more sophisticated capabilities such as the ability to make backups of copy protected discs and even the power to simultaneous duplicate to multiple recorders. But remember that the ability of a system to copy specific disc formats depends upon the individual capabilities of the software, reader and recorder used. It is therefore advisable to check with the respective manufacturers for specific information. |
| Typically, discs are duplicated CD to CD by using the computer’s CD-ROM or DVD-ROM drive as the master source feeding the copying recorder. In cases where a separate reading drive is not available the master is first downloaded to the computer hard drive using the reading ability of the recorder and later written back to a blank disc using the same recorder. Employing the hard disk as an intermediate copying step is also a common tactic used when dealing with poor quality source discs or other situations where computer systems are not fast enough to keep up to the speed set on the recorder. |
| CD Duplication Systems |
| For copying larger numbers of discs various dedicated CD duplication solutions are available including machines that function by themselves or with the assistance of an operator. These configurations can either sit as standalone units or may be attached as computer peripherals. The most common devices are hand-fed tower systems which employ a number of CD-R or CD-R/RW recorders chained together for simultaneous duplication from either a master CD or from a hard drive. Also widely used are automated products incorporating robotic disc handling systems which mechanically load and unload one or more recorders. Sometimes disc label printers are included to produce a handful or even hundreds of finished discs per hour. Historically large and expensive, many CD duplication systems are now compact and affordable and within reach of many for personal and office use. A number of companies also offer commercial CD duplication services to perform short run work in quick turnaround times. |
| CD Mass Replication |
| In contrast to CD duplication which is usually performed on a small scale at the desktop level, CD mass replication is typically used to make huge quantities of discs such as commercial audio CDs and software CD-ROMs. These prerecorded (pressed) discs are manufactured from a mold in a factory setting and are created using a series of industrial processes including premastering, mastering, electroplating, injection molding, metallization, spin coating, printing and advanced quality control. In addition to manufacturing discs many replication companies offer companion services including packaging, printing, distribution and fulfillment. |
| What is CD publishing? |
| Somewhat like CD duplication equipment, CD publishing systems employ CD-R or CD-R/RW recorders but are used to create quantities of unique discs from different computer files rather than just to make multiple copies of a single master disc. Employing robotic disc handling systems and integrated label printers, many of these devices can be accessed over computer networks and shared much like office laser printers. Examples of CD publishing applications include retail audio CD vending kiosks, creating CD-Rs containing cheque images or monthly banking records, archiving computer-generated billing records to disc in place of microfilm and accepting conventional 35 mm film resulting in digital pictures on CD-R discs. |
| Can CD-R and CD-RW discs be protected against copying? |
| Historically, copy protection technologies were only available to protect prerecorded (pressed) discs but a variety of methods are now available to deter copying the contents of CD-Rs and CD-RWs, to authenticate media and even to forensically trace the origin of discs. Such capabilities are included in some CD-R and CD-R/RW recorders or may be offered as features in software tools as well as duplication and publishing systems. |
| What is a Multisession CD-R or CD-RW disc? |
| Multisession recording allows additional data to be written to a previously partially recorded CD-R or CD-RW disc. Each session on the multisession disc has its own Lead-In Area, Program Area and Lead-Out Area and may be connected to other sessions to function as a single volume (linked) or operate independently (multi-volume). In addition to being written by a recorder the first session of a multisession disc can be, alternatively, prerecorded (stamped) at the factory. |
| What is the difference between fixation and finalization? |
| Fixation is the process of completing a CD-R or CD-RW disc session by writing Lead-In (table of contents) and Lead-Out information. Once a disc is fixated it can then be played back in CD and DVD-ROM drives and recorders and consumer electronics devices compatible with the particular disc type and format. It is also possible to record additional information later to create a multisession disc. Finalization, on the other hand, completely closes the disc so no further material can be added. |
| What are the different writing modes? |
| CD-R and CD-R/RW recorders employ several different writing modes including Disc-At-Once (DAO), Track-At-Once (TAO), Session-At-Once (SAO), and packet writing. Be aware that not all recorders and software support all writing modes. If in doubt, consult with the product manufacturer. During DAO recording the Lead-In Area, Program Area and Lead-Out Area of a CD-R or CD-RW disc are consecutively written in a single uninterrupted operation. DAO recording is only possible using a blank disc and, after recording is completed, no additional information can be written. Typically, DAO is used to write CD audio, CD-Text and discs destined for mass replication. In contrast to DAO, TAO operates by turning the writing laser on and off at the beginning and end of each track and writes the Program Area of a disc before its Lead-In and Lead-Out Areas. It is possible to use a recorder to read from (or write additional tracks to) a TAO disc before a session is fixated. All TAO discs contain 2 to 3 second gaps between tracks (run-in, run-out and link blocks) but some recorders have the ability to vary the size of the gaps. SAO is much like DAO in that the Lead-In Area, Program Area and Lead-Out Area are consecutively written in a single uninterrupted operation. However, the first session is not finalized so additional sessions can be added. Typically, SAO is used to write CD Extra (Enhanced Music CD) discs where the first session contains one or multiple audio tracks and the second session consists of multimedia computer data. Packet writing records variable (CD-R) or fixed (CD-RW) sized chunks or “packets” of data to the disc for as many times as is needed to complete the writing of the user’s files. In the case of a CD-R disc (which is not erasable) data may be added incrementally until the disc becomes full. CD-RW discs, on the other hand, are completely rewritable and thus are a little different from their CD-R cousins in that files can be added and deleted as needed. |
| What types of devices write CD-R and CD-RW discs? |
| All CD-R and CD-R/RW recorders write CD-R discs but only CD-R/RW recorders write both CD-R and CD-RW discs. Many DVD recorders also come combined with CD-R and CD-RW writing functions but be aware that there are exceptions. If in doubt, consult with the hardware manufacturer. |
| What do the numbers describing a CD-R or CD-R/RW recorder mean? |
| Manufacturers typically use a sequence of two, three or four numbers to express the maximum writing and reading speeds of a recorder. The generally accepted industry convention for a CD-R recorder has been for the first figure to indicate CD-R writing speed followed by CD reading speed for CD-R and prerecorded (pressed) data CDs. For a CD-R/RW recorder the first number usually indicates CD-R writing speed followed by CD-RW writing speed and then by the CD reading speed. In the case of a combination recorder a fourth number is included to indicate DVD reading speed. As examples, 8x12 usually means 8x CD-R write and 12x CD read while 48x12x48 typically indicates 48x CD-R write, 12x CD-RW write and 48x CD read. And for a combination recorder 24x10x40x12 denotes 24x CD-R write, 10x CD-RW write, 40x CD read, and 12x DVD read. |
| What types of CD-R and CD-R/RW recorder configurations are available? |
| Whether for PC, Mac or UNIX computers in desktop, laptop or notebook form, CD-R and CD-R/RW recorders are available in a wide variety of configurations to suit most needs. Several industry standard interfaces are available including SCSI, EIDE/ATAPI, Parallel, USB and IEEE 1394 for either internal or external recorder connection. |
| What is buffer underrun? |
| An important point to remember about CD-R and CD-RW recording is that information must be written to a blank disc in a continuous stream. To help smooth out the flow in the data transfer rate from the computer, the recorder employs a memory buffer which, like a reservoir storing water for use when it is needed, caches data for when it is required by the recorder. As with a water reservoir, the key is to always have enough data in the buffer to satisfy the demands of the recorder, even if, from time to time, the computer can’t supply the needed amount of information. If the buffer runs dry (a “buffer underrun”) the disc is ruined. |
| How can buffer underrun be prevented? |
| Most current computer recorders incorporate advanced buffer underrun protection technology to eliminate buffer underruns but for units not so equipped there are a variety of common sense techniques that can be used to help minimize the possibility. These include ensuring that the recorder and writing software are properly configured, defragmenting the operating system and data source hard disk partitions, disconnecting from any networks, closing all other programs and disabling background tasks such as power managers and anti-virus software. In more stubborn cases additional measures to be considered include reducing writing speed as well as enabling the recording software to build a temporary image on the hard disk drive before recording. |
| What is buffer underrun protection? |
| In order to keep pace with the demands of ultra speed writing, recorder manufacturers have created new technologies for preventing buffer underruns. A recent innovation now known by a multitude of different trade names, buffer underrun protection utilizes a combination of recorder hardware, firmware and writing software to accomplish its task. Buffer underrun protection functions by constantly monitoring the amount of data in the recorder’s buffer during the writing of a disc and suspends recording if the amount available falls below a predetermined threshold. Once the buffer again accumulates sufficient data the recorder resumes writing precisely where it left off. Obviously, it’s critical to leave as small a gap as possible between the previous and newly recorded sections so as to avoid producing an unreadable segment on the disc. Generally speaking, the gap length has been found to be well within the error correction capabilities of CD and DVD-ROM drives and players. As the technology matures the gap will continue to shrink. |
| Is special software needed to use CD-R and CD-R/RW recorders? |
| The two main types of software needed to operate CD-R and CD-R/RW recorders, namely packet writing software and CD recording software (sometimes called premastering software), are available for most major operating systems. The majority of CD-R and CD-R/RW recorders include either one or both types as part of their purchase bundles. Be aware, however, that software from competing publishers may offer a different range of features. In addition, some current operating systems and standalone application software have built-in CD-R and CD-RW recording capabilities. |
| CD Recording Software |
| Unlike many removable storage solutions that are restricted to just housing and retrieving data, CD-R and CD-R/RW recorders are also used as powerful multimedia devices. In addition to providing the means to store, backup and distribute data on CD-R and CD-RW discs, many CD recording software packages also include the tools necessary to write or edit different content on CDs such as music, photos and video. Taking the form of standalone applications, many recording software packages have the capability to create discs in different physical formats (eg. data, audio, video, hybrid, etc.) using various file systems (eg. UDF, ISO 9660, HFS, etc.) and support different file naming conventions (eg. Joliet, Rock Ridge, Apple extensions, etc.). Some can actually clean up clicks, pops, scratches and hiss from old music LPs or cassettes and lay out and print labels and jewel case inserts to personalize and identify discs after they are written. Depending upon the package, other capabilities may include the ability to duplicate CDs, assemble Red Book CD-DA or compressed digital audio compilation CDs a track at a time from different sources and even create photo and video albums. |
| Packet Writing Software |
| Packet writing software installs at the driver level and makes a CD-R or CD-R/RW recorder seem to the user as just another removable drive. Appearing the same as a floppy or hard disk, users write files to a CD-R or CD-RW disc by simply dragging and dropping the files over the recorder’s icon or saving from within an application. As with all removable storage systems, the first step in operating a CD-R or CD-R/RW recorder using packet writing software is to initialize the disc to prepare it to receive the user’s data. After inserting a blank disc into the recorder the user is prompted by the computer to initialize the disc which is then ready to go after an automatic formatting procedure. Some products conduct background formatting where the disc is available to write shortly after initiating the process but others require formatting to complete before data can be written. Packet writing records variable (CD-R) or fixed (CD-RW) sized chunks or “packets” of data to the disc for as many times as is needed to complete the writing of the user’s files. In the case of a CD-R disc (which is not erasable) data may be added incrementally until the disc becomes full. CD-RW discs, on the other hand, are completely rewritable and thus are a little different from their CD-R cousins in that files can be added and deleted as needed. Typically, packet writing software records CD-R and CD-RW discs in OSTA’s Universal Disc Format (UDF). |
| What is the storage capacity of CD-R and CD-RW discs formatted for packet writing? |
| After being formatted for packet writing use the storage capacity of CD-R and CD-RW discs is somewhat less than their unprepared state. For example, a 74 minute/650 MB (12 cm) CD-R disc has an initial formatted capacity of roughly 620 MB while an equivalent CD-RW disc stores approximately 530 MB after being formatted for random rewriting. Due to increased defect management overhead, a Mount Rainier formatted CD-RW disc is able to store roughly 30 MB less than its conventionally packet written counterpart. |
| Are CD-RW discs created using packet writing software from different publishers compatible with each other? |
| Generally speaking, it is possible to format a CD-RW disc using one publisher’s packet writing software and write to the same disc using software offered from a different publisher. However, once data has been written to the disc only the software that was used to write the information can be used to append or rewrite other data. Greater writing interchangeability for CD-RW discs is, however, one of the primary goals of the new Mount Rainier format. It is advisable to consult with the appropriate software publisher for specific compatibility details. |
| What alternatives are available to label CD-R and CD-RW discs? |
| There are several different labeling methods available for CD-R and CD-RW discs ranging from hand writing, to adhesive labels, specialized devices that print directly onto the disc surface and ultimately the various commercial printing solutions. Each option is distinguished by cost, speed and convenience as well as by durability and the visual quality of the result. But keep in mind that applying any kind of label modifies the disc in a significant way. Thus, product warranties can be affected and unforeseen consequences may arise. It is, therefore, advisable to always follow manufacturer directions. |
| Hand Writing |
| By far the quickest and least expensive way to label a disc is to simply write on its top surface. Using a soft fiber or felt-tipped permanent marker is preferable but be aware that the solvents in some types of inks can migrate through the disc surface and potentially damage the reflective and dye layers beneath. The part of the disc least vulnerable to injury is the center clamping or hub area. Beware ballpoint pens or other sharp writing instruments as they may deform the disc substrate and delaminate the disc layers thereby causing information to become unreadable. Some discs are specially coated to accommodate handwritten labels and even some special markers are available and intended for such use. |
| Adhesive Labels |
| A more attractive way to label a disc is to apply an adhesive label. Several manufacturers offer inkjet and laser printer compatible products specifically designed for labeling discs as well as positioning devices to help with centering. Full surface or “donut-style” labels are preferable to partial stickers but be aware that any adhesive label can potentially upset the balance of a disc when playing back, especially at high speeds, causing excessive noise, vibration and data retrieval problems. Heat, humidity, handling and the passage of time can also compromise the stability of adhesive labels causing separation from the disc surface and even interfere with the drive. Sticky labels may not be the best choice when archiving important data as some types of label adhesives can react with and compromise the disc over time. Remember too that, once applied, labels should never be removed or repositioned. Even smoothing air bubbles can concentrate physical stresses in a small area and delaminate the disc. |
| Specialized Disc Printers |
| A range of specialized disc printing devices is also available to label discs in larger numbers and for imparting a more polished appearance. Currently, desktop products employing inkjet, thermal transfer and re-transfer technologies are available for directly labeling on the disc surface. |
| Inkjet |
| Inkjet printing technology has been available for many years and has proven extremely popular with consumers due to its high quality and cost effectiveness. Inkjet printers function by ejecting liquid ink from a print head onto the surface of a specially coated “inkjet-printable” disc. These special discs have an extra coating, called an Ink Absorption Layer (IAL), which receives the ink from the printer and allows it to stay in place long enough to dissipate its solvents and properly dry. Inkjet printers produce high-resolution full color images but there is a downside in that resulting labels can be smudged by high humidity or damp fingers. Inkjet printed discs should not be stored or shipped in form-fitting soft plastic envelopes as the chemicals used to keep the package materials supple can soften the inks causing the label to stick to the sleeve and potentially delaminate the disc when removed. Using jewelcases or other containers that do not come into direct contact with the printed surface is best. |
| Thermal Transfer |
| Unlike inkjet printers which spray liquid ink, thermal transfer printers convey solid pigment from a coated ribbon onto the surface of a disc through a combination of heat and pressure. Typically used to produce monochrome and spot color labels, thermal transfer printing does not require specially coated discs to accept the ink from the printing process. The results are, as well, reasonably durable. However, some disc surfaces give better results than others and offer more protection from potential damage during the printing process. Consequently, discs are available which feature special coatings optimized for thermal transfer printing. For labeling situations where discs share a largely common background appearance but vary slightly from disc to disc or among groups of discs some thermal transfer solutions can align and overprint their output onto partial images already screen printed onto the surface of the disc. |
| Commercial Printing |
| Various methods are used to commercially decorate discs including screen, offset, pad and flexographic printing. These are large-scale industrial processes typically used to label large numbers of discs with the same pattern or in situations when precise color matching is required for critical items such as company logos. In addition to desktop disc labeling, many duplication companies and replicators offer commercial printing services. |
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