• Red Book
• Yellow Book
• Orange Book
• Green Book
• Blue Book
• White Book

The "books" of the Compact Disc family were named for the color of the binder covers in which the specification was issued. Red Book is the specification for CD Audio, Yellow Book is CD-ROM, Orange Book is CD Recordable, Green Book is CD interactive (CD-i), Blue Book is Enhanced CD and White Book is Video CD. All of these books are based on the Red Book physical disc specification, but some also define the types of content the disc may contain, such as 44.1 MHz PCM audio for Red Book, and MPEG 1 video for White Book. Other disc formats, such as Mixed Mode or HFS, do not have books, but are logical variations of the one or more of the book formats. For example, the Yellow Book defines CD-ROM as far as the physical characteristics of the disc, addressing schemes, and error correction are concerned, but the file system and type of content can be user defined. A Yellow Book disc could use the HFS file system, the ISO 9660 file system, or a user-defined file system, and could contain text, raw data, or multimedia elements. 

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RED BOOK - Compact Disc Audio

Red Book, which defines CD-Audio, is the compact disc patriarch. Compact disc was created, after all, to be nothing more or less than a universal delivery medium for one type of content only, namely music digitized at 44,100 samples per second (44.1KHz) and in a range of 65,536 possible values (16 bits). Red Book, or Compact Disc-Digital Audio (CD-DA), was defined by Philips N.V. and Sony Corporation in 1980.

Data on an audio disc is organized into frames in order to ensure a constant read rate. Each frame consists of 24 bytes of user data, plus synchronization, error correction, and control and display bits. One of the first crucial things to understand about CD-Audio is that its data is not arranged in distinct physical units. Instead, one frame is interleaved with many other frames so that a scratch or defect in the disc will not destroy a single frame beyond correction. Rather, a scratch will destroy a small portion of many frames, all of which can be recovered.

Red Book disc itself is divided into three areas: Lead In, Program, and Lead Out. Each track's location, or address, is recorded in the disc's TOC, or Table of Contents, which is stored in the Lead In area of every disc. Because pressed CDs are read-only, the number and location of the audio tracks to be recorded is known in advance, and the TOC is written to the disc (or more accurately, to the glass master that will be used to create metal stampers to mold discs) in advance of writing the actual audio data. An audio disc can contain up to 99 tracks, which are stored in the Program area. After the Program area is the Lead Out area, which is simply 90 seconds of silence, or blank sectors. The Lead Out area on an audio disc is essentially just a ham-fisted way to let CD-Audio players know the music is over.

All of this technical detail about Red Book would be eminently forgettable, except for one small fact: the Red Book specification is the base case for all other types of compact disc. Every disc that came after Red Book in the CD family includes the specs of  Red Book or refers to them. The physical, logical, and content description details of Red Book are the basic DNA of the compact disc, and everything that follows is either a specialization of these details, an adaptation, or a work-around. For example, the original strategy of data layout for safekeeping--interleaving files--shows up as a big factor in the fixed-length versus variable-length packet writing, in the current efforts behind the adoption of UDF (the Universal Disk Format) for CD-RW (CD-Rewritable). Packet writing for rewritability is just one instance of how all issues with compact disc come back to the father of all compact discs, Red Book. (Some argue, it is true, that the children may suffer for the sins of the father.)

YELLOW BOOK - CD ROM

If Red Book is the father of all CD formats, Yellow Book is the mother. Red Book is actually the basis for and an integral part of Yellow Book, which defines CD-ROM, or Compact Disc-Read Only Memory, announced by Philips and Sony in 1983. CD-ROM was envisioned as a way to allow digitized content including but not limited to audio to benefit from the capacity, durability, and  economies of scale that were rapidly making compact disc audio a big success. Yellow Book is the disc specification that gave birth to all the variations on a CD theme that make CD formats so versatile and, equally, so confusing.

Rather than rewrite the physical format, it was decided to adapt the physical format of Red Book for the storage of computer data. At its lowest level, Yellow Book specification for CD-ROM is nearly identical to RedBook, in that it retains the TOC, Lead In, Program area, Lead Out, and basic error correction. But the next level of Yellow Book organizes the frames defined in Red Book into sectors (98 frames, or 2,352 bytes, equalsone sector) and adds another layer of error detection and correction. The extra error correction information, at 288 bytes per sector, plus 12 bytes of sync and 4 bytes of header, reduces the available sector space for user data to 2,048 bytes. Addresses of sectors are expressed as minutes, seconds, and sectors (MM:SS:SS). Yellow Book stops there, however, leaving it up to the CD-ROM developer to decide how to arrange sectors into logical blocks and logical blocks into files. And that is the first step into the complexity of CD, in the form of Mode 1 and Mode 2.

The Yellow Book specification defines two data structures: Mode 1 and Mode 2. The mode byte, which is included in the header field of a CD-ROM sector, describes the type of data contained in the data field. Mode 1 denotes CD-ROM data with Error Correction Code (ECC), which provides room for 2,048 bytes of user data and is the mode used to store data that is unforgiving of error, like computer programs or databases. Mode 2 denotes a sector with data stored without ECC, which provides more room (2,336bytes) for user data, but which is typically used for data that is more tolerant of error, like audio, video, or graphics.

Most CD-ROM titles that hold databases, shareware archives, and computer programs are Yellow Book, Mode 1, and most CD-ROM discs published--period--are in "plain-vanilla" Yellow Book, Mode 1, ISO 9660 Level 1, for the DOS or Windows platform. These discs are also "accessible" on Macintosh and UNIX platforms, but they don't appear or perform like Apple or UNIX "natives. "In spite of and because of this, the plain vanilla CD-ROM is the single most standardized data storage medium ever created.

Mode 2 is a way of interleaving sectors of data with extra error correction (Form 1) with sectors of data without extra error correction (Form 2), since Mode 1 does not allow unlike sectors to reside in the same session on a disc. The Mode 2 branch of the family tree is the show-biz side. CD-ROM/XA, Bridge discs (including Photo CD, Karaoke CD, and Video CD), and GreenBook, or CD-i, are performing cousins to the computer CD-ROM. They have something in common besides Mode 2: they are all intended to play on dedicated consumer electronics platforms. Some, like Photo CD and Video CD, will play on either a computer or a dedicated platform such as a CD-i player, a Video CD player, or a dedicated Photo CD player (if you could find one).

In the early days of CD-ROM publishing, each developer used a different, incompatible file format for CD-ROM. This problem was addressed by the High Sierra Group, an ad hoc committee of CD-ROM developers who created the High Sierra Format, which was later adopted, with minor revisions, as ISO 9660, the logical file format for CD-ROM. There are three Levels of Interchange within ISO 9660:  Level 1 requires that each file be recorded as a continuous stream of bytes, with filename conventions that are similar to the restrictions of DOS;  Level 2 relaxes the filenaming conventions, among other things; and Level 3 is anything goes.

ISO 9660 was what gave rise to the claim "any disc plays in any drive" for CD-ROM. Unfortunately, the lowest common denominator approach in ISO9660-Level 1-was not optimal for operating systems other than DOS. Apple's long filenames and data and resource forks, and UNIX's deep directory structures did not fit well into the ISO 9660 Yellow Book mold. But even as the seemingly rigid Red Book could be adapted to do what it was never designed to do, so could ISO 9660 be adapted to suit the purpose.

Joliet, Rock Ridge Interchange Protocol, and Apple Extensions are three extensions of ISO 9660 that permit CD-ROM applications to retain cross-platform compatibility while performing like natives in their respective operating systems, whether Windows 95, UNIX, or Apple HFS.

And then there is hybrid disc, which is a disc that will work in two or more platforms, operating systems, or environments. Partitioned hybrids contain two or more separate partitions, each containing a complete setof data, each formatted for different operating systems. Shared Hybrid is a type of CD-ROM that also works on two or more operating systems, but each operating system accesses a shared data set. The disc contains one partition, containing the complete data set and all the files necessary for each operating system, but the DOS or Windows (or UNIX) user sees only the files pertinent to that environment, and the Macintosh user sees only the files pertinent to Macintosh. As if there weren't enough types of hybrids already, the term "hybrid" is also being used at times for a disc that includes Internet access along with an application that works locally. Sometimes this type of disc is called a Web hybrid, or CD/online hybrid.

ORANGE BOOK CD Recordable

Orange Book, Part II (Part I was about MO or magneto-optical drives) added a whole new dimension to the CD family, which was the ability to create a disc in a desktop environment. The time of Orange Book's first publication was 1988, and the authors were, again, Philips and Sony. The ramifications for the CD clan could hardly have been more radical.

No longer a non-recordable read-only medium whose use was limited to applications restricted by the "lots of static information to lots of users" rule of thumb of replicated media, the recordable CD placed the power of publishing on disc in the hands of individuals with a personal computer and a CD recorder. It was as if the entire CD family had suddenly developed a genetic ability to fly, where once only walking was possible.

Not only was the disc now recordable, it was soon also appendable. The medium that was at first engendered only as a mass-produced vehicle for linear, read-only music of a very specific type was now capable of being used as a recordable and appendable medium for all types of random access data.

There was a price to pay, of course, for this specialized adaptation of the original disc, and unfortunately that price was paid in compatibility.The power of recording discs on the desktop was a package deal and brought with it the responsibility of making discs that would work. As the specialization developed, so did the uses to which the specialization could be put; this only increased the compatibility problem, even though improvements in reliability kept pace with the proliferation and specialization of the recordable disc.CD-Recordable grew into its new abilities, though, and has not only enjoyed conspicuous success in its own right, but brought increased distinction to its forebears.

One key issue for CD-Recordable was the shift from single-session or Disc-at-Once (DAO) writing to multisession, whether in the form of Track-at-Once (TAO), multivolume multisession, linked or appended multisession, or, in the latest twists, various packet writing schemes. Adapting the ROM medium of CD exacts several prices, including the multimegabyte overhead needed to work around the stamped-at-once original nature of CD. The ability to write different data recording sessions can use up to 15MB each time for LeadIn and Lead Out alone; keep in mind that Lead In goes back to CD-Audio's need for a place to store the TOC with addresses to let players know where music tracks begin; Lead Out helps CD-ROM drives with read-ahead caching, to figure out, when it comes right down to it, where the read head has been. Nobody ever claimed retrofitting standards was a pretty business.

GREEN BOOK - Compact Disc Interactive

The Green Book specification for CD-i (Compact Disc Interactive) is unique in the CD family tree: it is the only specification which defines not only the disc and the contents, but an entire hardware and software system, a variety of special compression methods for audio and visual data, and a method of interleaving audio, video, and text data. CD-i has found a niche in informational and marketing kiosks, training, and portable interactive sales presentations, and is especially well suited for the presentation of high-capacity interactive multimedia applications to the non computer literate. CD-i is designed to interface with televisions and stereo systems. A $200 component called an FMV cartridge can be installed to add VHS quality, full-screen, full-motion video capabilities to existing CD-i players. A relatively recent development in CD-i is the addition of a modem, which allows a CD-i player to include a World Wide Web connection.

And where CD-i, or Green Book, went, soon followed CD-ROM/XA, which was an extension to Yellow Book specifications that was finalized in 1989 by, of course, Philips and Sony, but with help from Microsoft Corporation. CD-ROM/XA defined CD-ROM titles that shared certain common traits with CD-i titles--especially the data interleaving, interactive capabilities, and a specific form of audio compression (ADPCM). The point of CD-ROM/XA was to describe a standard means for making multimedia data access from CD more efficient; interleaving audio and video data, for example, allows for better synchronization as long as the audio isn't Red Book, which is placed on its own track. CD-ROM/XA was also called a "bridge disc"--a disc that could be played on both a CD-i machine and a PC--because of this overlap.

BLUE BOOK - CD Plus

The Orange Book specification for CD-R allows a CD-R disc to be recorded in more than one session, rather than "Disc-at-Once," or as a single volume. The multiple sessions and tracks on the CD-Recordable disc can be recorded as entirely separate volumes, or so that each separate session contains "pointers" to link the information in earlier sessions to later sessions. Depending on the recording method, the resulting disc could appear as a logical whole, or as discrete sessions. These discrete, or linked, sessions could be Yellow Book or Red Book, in any order. Thus, it is possible to create a disc that places audio data in the first track of the first session of the disc, where it can be recognized and played by CD-Audio players, and CD-ROM data in the second session of the disc, where it can only be accessible by CD-ROM drives controlled by personal computers. In May 1995, Philips announced a specification to define "stamped multisession" discs. A subset of that specification, designed expressly for stamped multisession discs limited to two sessions (one music, one data), will soon be released as a new color book (Blue Book) and called CD Plus.

As obvious and elementary as it may seem to use multisession for enhanced audio applications, there are some stumbling blocks. First and foremost is the fact that replicators of CDs are not yet equipped to mass produce "stamped multisession" discs with any kind of reliability. The software used to create glass masters for the various disc formats-Red Book, Yellow Book, etc.-does not, as yet, include support for multisession. Equipment that verifies masters and performs quality testing for finished discs is not set up to verify stamped multisession discs.

The advantage to CD Plus is that it is a single, defined, licensed standard supported by Philips, Sony, Microsoft, and Apple. It plays on CD-Audio players with no possibility of producing static and on many newer computers with CD-ROM drives. The disadvantages are that there are many existing CD-ROM drives-approximately 40% of the installed base-that are not capable of playing multisession discs. Even existing multisession drives may require a driver upgrade in order to use these discs. CD-ROM data is stored at the outer edge of the disc-not prime real estate for fast, error-free playback.

WHITE BOOK - Video CD

The White Book specification for Video CD, which was announced by JVC, Philips, SONY and Matsushita in July 1993, is a special implementation of CD-ROM/XA designed to store MPEG-1 video. MPEG stands for Motion Picture Experts Group, which is a joint committee of the International Standards Organization and the International Electrochemical Commission. The White Book specification defines a Mode 2, Form 2 disc that can contain up to 74 minutes of VHS-quality, full-screen, full-motion video. Video CD can be played on a personal computer with a CD-ROM/ XA drive and an add-in MPEG video card, a CD-i player with an FMV cartridge, modified stand-alone VideoCD players available from several electronics manufacturers, many DVD players or with software video decoding only. In Southeast Asia, VideoCD has entirely replaced the VHS tape for movie sales and rentals.

The problems with storing video data on compact discs are twofold: too much data and a slow rate of output. One second of uncompressed VHS-quality video would require five megabytes of storage space. A 680MB compact disc could contain about two minutes of video. Obviously, the data must be compressed for storage, then decompressed for real-time display. MPEG-1 uses various techniques to compress video data by a factor as high as 200:1.

Because MPEG is an international standard, any manufacturer can make hardware capable of recording, compressing, and playing MPEG video. Because it is not limited to any one platform, MPEG video can also be recorded and played back from Red Book and Yellow Book CDs, given the necessary hardware and interface. MPEG can be used by any CD-ROM publisher to include video clips in multimedia applications. The rates of video and audio compression can be varied according to the application. However, VideoCD extends MPEGs usefulness by authoring the video in standard bitrates into a format that removes redundant MPEG1 video information, and adding a CDi runtime application for use in CDi, DVD or VideoCD players. Many CD-ROM formatting packages claim to format VideoCDs, but do not include this required CDi application and also do not offer interactive authoring capabilities.

The White Book, since its original inception as version 1.1, has been supplemented over the years by VideoCD 2.0 (1995), VCD-ROM (1997), VCD-Internet (1997) and SuperVCD (1998). VideoCD 2.0 is for interactive PAL and NTSC video, including hi-resolution stills and fastforward/rewind capabilities. VCD-ROM allows for creation of hybrid CD-ROM and VideoCD discs. VCD-Internet is a standardized way to 'link' video and the webpages coming from the disc or on-line. SuperVCD is hi-bitrate MPEG1 and/or variable bitrate MPEG2, using inexpensive CD-R drives and media instead of DVD drives.