Understanding CD-R & CD-RW

PHYSICAL, LOGICAL AND FILE SYSTEM STANDARDS

What is the Orange Book?
Orange Book is the set of specifications created by Philips and Sony to define the optical signal characteristics, physical arrangement, writing methods and testing conditions for CD-R (Orange Book Part II) and CD-RW (Orange Book Part III) discs. First released in 1990, Orange Book originally dealt with only single speed CD-R recording but, with rapid advances since made in hardware and media technology, the specification grew to include CD-RW in 1996. Higher writing speeds continue to be incorporated as the industry evolves.

What are the different sections of CD-R and CD-RW discs?
Orange Book organizes CD-R and CD-RW discs into various sections serving distinct purposes. The Information Area is most fundamental and consists of a shallow spiral groove (pregroove) extending from the discs’ inside to outside diameter. Encoded in the structure of this pregroove are speed control and Absolute Time In Pregroove (ATIP) time code information as well as other parameters critical for recorders to correctly write a disc. Several regions within this pregroove are reserved exclusively for recorder use.

The first is the Power Calibration Area (PCA), located in the inner portion of the disc, which is employed while determining the correct power level for the writing laser. Due to physical and practical design limitations on rotational velocity it is, generally speaking, not possible to conduct power calibrations at the inner diameter of the disc at speeds above 16x. A process of extrapolation is therefore used to determine suitable writing power for those higher speeds. Recently, Orange Book has designated the addition of another PCA located in the Lead-Out Area at the outer portion of the disc to provide the space necessary to conduct actual high speed write power calibrations.

Following the first PCA is the Program Memory Area (PMA) which is used as intermediate storage to record track information for all sessions written to the disc. Typically, the PMA is first followed by the Lead-In Area, containing table of contents information, followed by the Program Area which holds the written data tracks and finally the Lead-Out Area which indicates to a reading device that the end of the data has been reached.

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 is ISO 9660?
The ISO 9660 standard was introduced in 1988 and is the most widely used file format for data (CD-ROM) discs. ISO 9660 defines a common logical format for files and directories so discs written to ISO 9660 specifications can be read by a wide array of computer operating systems (MS-DOS, Windows, Mac OS, UNIX, etc.) as well as consumer electronics devices. Due to the vast differences which exist among native file systems ISO 9660 takes a lowest common denominator approach resulting in a variety of restrictions upon the nature and attributes of files and directories. Three levels of interchange define these restrictions with level one being the most constraining and level three is the least (at the cost of compatibility with some operating systems). Various protocols are available to extend ISO 9660 to accommodate file system features specific to individual operating systems (longer file names, deeper directory structures, more character types, etc.) while preserving ISO 9660 compatibility with other platforms. These protocols include Joliet (Windows 95 and higher), Apple Extensions (Mac OS) and Rock Ridge (UNIX).

What is The Universal Disc Format (UDF)?
The Universal Disc Format (UDF) specification was first released by OSTA in 1995 and is designed to be a common logical file system for all removable optical storage media. Over the years various updates to UDF have been introduced to add new capabilities. For example, UDF 1.02 is the standard file system used for prerecorded and recordable DVD discs while UDF 1.5 is commonly employed for packet writing CD-R and CD-RW media. Most recently, UDF 2.0 has added full support for Windows NT, enhanced data security and improved CD-R functions while defining backward read capabilities between discs created with the new UDF 2.0 format and discs created with earlier versions of UDF.

What is a hybrid disc?
The term “hybrid” is popularly used to describe several different types of discs. The first kind of hybrid disc is one that contains multiple file systems, such as ISO 9660 and HFS (Mac OS). A second type of hybrid is a CD that contains applications designed to interact with the Internet so static data resides on the disc and live information is downloaded as needed from the Web. These discs are sometimes called “connected CDs.” A third kind of hybrid is defined by Orange Book as a CD-R or CD-RW disc with a prerecorded (stamped) first session with the ability to potentially hold additional written sessions.

What is Running OPC?
Running Optimum Power Control (Running OPC) is a special technique used in many newer CD-R and CD-R/RW recorders that monitors and maintains the quality of the disc writing and ensures the accuracy of all the marks and lands lengths across the disc. The term Running OPC actually describes the general process that may be known by several trade names. Some differences in execution may be present to give some of these implementations competitive advantages over others.