After Philips and Sony created the Red Book CD-DA format, they began work on other format standards that would allow CDs to store computer files, data, and even video and photos. These standards control how the data is formatted so that the drive can read it, and additional file format standards can then control how the software and drivers on your PC can be designed to understand and interpret the data properly. Note that the physical format and storage of data on the disc as defined in the Red Book was adopted by all subsequent CD standards. This refers to the encoding and basic levels of error correction provided by CD-DA discs. The other "books" specify primarily how the 2,352 bytes in each sector are to be handled, what type of data can be stored, how it should be formatted, and more.

All the official CD standard books and related documents can be purchased from Philips for $100$150 each. See the Philips licensing site at www.licensing.philips.com for more information.

Red Book CD-DA

The Red Book introduced by Philips and Sony in 1980 is the father of all compact-disc specifications because all other "books" or formats are based on the original CD-DA Red Book format. The Red Book specification includes the main parameters, audio specification, disc specification, optical stylus, modulation system, error correction system, and control and display system. The latest revision of the Red Book is dated May 1999.

Yellow BookCD-ROM

The Yellow Book was first published by Philips, Sony, and Microsoft in 1983 and has been revised and amended several times since. The Yellow Book standard took the physical format of the original CD-DA, or Red Book, standard and added another layer of error detection and correction to enable data to be stored reliably. It also added additional synchronization and header information to enable sectors to be more accurately located. Yellow Book specifies two types of sectoringcalled Mode 1 (with error correction) and Mode 2which offer different levels of error detection and correction schemes. Some data (computer files, for example) can't tolerate errors. However, other data, such as a video image or sound, can tolerate minor errors. By using a mode with less error correction information, more data can be stored, but with the possibility of uncorrected errors.

In 1989, the Yellow Book was issued as an international standard by the ISO as ISO/IEC 10149, Data Interchange on Read-Only 120mm Optical Discs (CD-ROM). The latest version of the Yellow Book is dated May 1999.

Green Book CD-i

The Green Book was published by Philips and Sony in 1986. CD-i is much more than just a disc format; instead it is a complete specification for an entire interactive system consisting of custom hardware (players) designed to be connected to a television, software designed to deliver video and audio together with user interactivity in real time, and the media and format. A CD-i player is actually a dedicated computer usually running a variant on the Motorola 68000 processor line, as well as a customized version of the Microware OS/9 Real Time Operating System.

CD-i enables both audio and video to share a disc and enables the information to be interleaved so as to maintain synchronization between the pictures and sounds. To fit both audio and video in the same space originally designed for just audio, compression was performed. The video was compressed using the Moving Picture Experts Group-1 (MPEG-1) compression standard, whereas the audio was compressed with adaptive differential pulse code modulation (ADPCM). ADPCM is an audio encoding algorithm that takes about half the space for the same quality of standard PCM, and even less if quality is reduced by lowering the sampling rate or bits per sample. Using ADPCM, up to 8 hours of stereo or 16 hours of mono sound can fit on one CD. The "differential" part of ADPCM refers to the fact that it records the differences between one signal and the next (using only 4-bit numbers), which reduces the total amount of data involved. ADPCM audio can be interleaved with video in CD-i (and CD-ROM XA) applications.

The Yellow Book defines two CD-ROM sector structures, called Mode 1 and Mode 2. The Green Book (CD-i) refines the Mode 2 sector definition by adding two forms, called Mode 2, Form 1 and Mode 2, Form 2. The Mode 2, Form 1 sector definition uses ECC and allows for 2,048 bytes of data storage like the Yellow Book Mode 1 sectors, but it rearranged things slightly to use the 8 formerly unused (blank or 0) bytes as a subheader containing additional information about the sector. The Mode 2, Form 2 definition drops the ECC and allows 2,324 bytes for data. Without the ECC, only video or audio information should be stored in Form 2 sectors because that type of information can tolerate minor errors.

All types of media were produced for CD-i, but because the files use the OS/9 file format, they can't be viewed by a PC without special drivers. One of the best resources for CD-i technical information, utility software, drivers, and emulators is The New International CD-I Association website at www.icdia.org.

Today, the CD-i format is largely obsolete. The last revision of the standard was produced in May 1994. Philips sold off its entire consumer CD-i catalog to Infogrames Multimedia in 1998, which now owns the rights for virtually all consumer CD-i titles ever produced. Philips made a final run of CD-i players in 1999, and it is doubtful any new ones will ever be produced. The legacy of CD-i lives on in the other formats that use specifications originally devised for CD-i, such as the Mode 2, Form 1 and Form 2 sector structures found in CD-XA and the MPEG-1 video format later used in the White Book (CD-Video).

CD-ROM XA

CD-ROM XA originally was defined in 1989 by Philips, Sony, and Microsoft as a supplement to the Yellow Book. CD-ROM XA brings some of the features originally defined in the Green Book (CD-i) to the Yellow Book (CD-ROM) standard, especially for multimedia use. CD-ROM XA adds three main features to the Yellow Book standard. The first consists of the CD-i-enhanced sector definitions (called forms) for the Mode 2 sectors; the second is a capability called interleaving (mixing audio and video information); and the third is ADPCM for compressed audio. The latest version of the CD-ROM XA standard was released in May 1991.

Interleaving

CD-ROM XA drives can 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 can 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. Without interleaving, the drive would have to read and buffer the entire video track before it could read the audio track and synchronize the two for playback.

Sector Modes and Forms

Mode 1 is the standard Yellow Book CD sector format with ECC and EDC to enable error-free operation. Each Mode 1 sector is broken down as shown below:

In the original Yellow Book, Mode 2 was defined as a sector without any ECC or EDC. Unfortunately, Mode 1 (which had ECC and EDC) couldn't be mixed with Mode 2 sectors on the same track (program or song). To enable data with and without error detection and correction in a single track, new sector format subsets for Mode 2 sectors were added in the Green Book (CD-i) and subsequently adopted in the CD-ROM XA extensions. This enabled information that would not tolerate errors (such as programs or computer data) to be interleaved or mixed within the same track with information that would tolerate errors (such as audio or video data). These variations on Mode 2 include Form 1 and Form 2 sectors. Each Mode 2, Form 1 sector is broken down as shown in the tables below:

Both Mode 2 sector formats add a subheader field that identifies the type of information (such as audio or video) carried in the user data field. The Form 2 sector lacks the ECC of the Form 1 sector and increases the size of the user data field instead. This type of sector is for storing audio or video data that can tolerate errors.

Because they don't use any third-level error correction, CD-ROMs that use the Mode 2, Form 2 sector format (such as MPEG video CDs) can hold more user information than other CD-ROM types in the same number of sectors and as a result also have a higher data transfer rate of 174.3KBps instead of the standard 153.6KBps. Note that Form 2 sectors are never used to store data or program files because errors can't be tolerated in that type of information. In that case, the Mode 2, Form 1 sector format would be used.

For a drive to be truly XA compatible, the audio data written in Form 2 sectors on the disc as audio must be ADPCM audiospecially 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.

Some earlier drives were called XA-ready, which meant they were capable of Mode 2, Form 1 and Form 2 reading but did not incorporate the ADPCM chip. This is not a significant shortcoming, however, because only certain multimedia titles use the ADPM encoding (with interleaved audio and video). The main benefit XA brought to the table was the additional sector modes and forms taken from the Green Book.

Orange Book

The Orange Book defines the standards for recordable CDs and originally was announced in 1989 by Philips and Sony. The Orange Book comes in three parts: Part I describes a format called CD-MO (magneto-optical), which was to be a rewritable format but was withdrawn before any products really came to market; Part II (1989) describes CD-R; and Part III (1996) describes CD-RW. Note that originally CD-R was referred to as CD-WO (write-once), and CD-RW originally was called CD-E (erasable).

The Orange Book Part II CD-R design is known as a WORM (write once read mostly) format. After a portion of a CD-R disc is recorded, it can't be overwritten or reused. Recorded CD-R discs are Red Book and Yellow Book compatible, which means they are readable on conventional CD-DA or CD-ROM drives. The CD-R definition in the Orange Book Part II is divided into two volumes. Volume 1 defines recording speeds of 1x, 2x, and 4x the standard CD speed; the last revision, dated December 1998, is 3.1. Volume 2 defines recording speeds up to 48x the standard CD speed. The latest version released, 1.2, is dated April 2002.

The Orange Book Part III describes CD-RW. As the name implies, CD-RW enables you to erase and overwrite information in addition to reading and writing. The Orange Book Part III CD-RW definition is broken into three volumes. Volume 1 defines recording speeds of 1x, 2x, and 4x times the standard CD speed; the latest version, 2.0, is dated August 1998. Volume 2 (high-speed) defines recording speeds from 4x to 10x standard CD speed; the latest version, 1.1, is dated June 2001. Volume 3 (ultra-speed) defines recording speeds from 8x to 32x; the latest version, 1.0, is dated September 2002.

Besides the capability to record on CDs, the most important feature instituted in the Orange Book specification is the capability to perform multisession recording.

Multisession Recording Overview

Before the Orange Book specification, CDs had to be written as a single session. A session is defined as a lead-in, followed by one or more tracks of data (or audio), followed by a lead-out. The lead-in takes up 4,500 sectors on the disc (1 minute if measured in time or about 9.2MB worth of data). The lead-in also indicates whether the disc is multisession and what the next writable address on the disc is (if the disc isn't closed). The first lead-out on a disc (or the only one if it is a single session or Disk At Once recording) is 6,750 sectors long (1.5 minutes if measured in time or about 13.8MB worth of data). If the disc is a multisession disc, any subsequent lead-outs are 2,250 sectors long (0.5 minutes in time or about 4.6MB worth of data).

A multisession CD has multiple sessions, with each individual session complete from lead-in to lead-out. The mandatory lead-in and lead-out for each session do waste space on the disc. In fact, 48 sessions would literally use up all of a 74-minute disc even with no data recorded in each session! Therefore, the practical limit for the number of sessions you can record on a disc would be much less than that.

CD-DA and older CD-ROM drives couldn't read more than one session on a disc, so that is the way most pressed CDs are recorded. The Orange Book allows multiple sessions on a single disc. To allow this, the Orange Book defines three main methods or modes of recording:

• Disk-at-Once (DAO)

• Track-at-Once (TAO)

• Packet Writing

Disc-at-Once

Disc-at-Once means pretty much what it says: It is a single-session method of writing CDs in which the lead-in, data tracks, and lead-out are written in a single operation without ever turning off the writing laser; then the disc is closed. A disc is considered closed when the last (or only) lead-in is fully written and the next usable address on the disc is not recorded in that lead-in. In that case, the CD recorder is incapable of writing any further data on the disc. Note that it is not necessary to close a disc to read it in a normal CD-ROM drive, although if you were submitting a disc to a CD duplicating company for replication, most require that it be closed.

Track-at-Once

Multisession discs can be recorded in either Track-at-Once (TAO) or Packet Writing mode. In Track-at-Once recording, each track can be individually written (laser turned on and off) within a session, until the session is closed. Closing a session is the act of writing the lead-out for that session, which means no more tracks can be added to that session. If the disc is closed at the same time, no further sessions can be added either.

The tracks recorded in TAO mode are typically divided by gaps of 2 seconds. Each track written has 150 sectors of overhead for run-in, run-out, pre-gap, and linking. A CD-R/RW drive can read the tracks even if the session is not closed, but to read them in a CD-DA or CD-ROM drive, the session must be closed. If you intend to write more sessions to the disc, you can close the session and not close the disc. At that point, you could start another session of recording to add more tracks to the disc. The main thing to remember is that each session must be closed (lead-out written) before another session can be written or before a normal CD-DA or CD-ROM drive can read the tracks in the session.

Packet Writing

Packet writing is a method whereby multiple writes are allowed within a track, thus reducing the overhead and wasted space on a disc. Each packet uses four sectors for run-in, two for run-out, and one for linking. Packets can be of fixed or variable length, but most drives and packet-writing software use a fixed length because dealing with file systems that way is much easier and more efficient.

With packet writing, you use the Universal Disk Format (UDF) version 1.5 or later file system, which enables the CD to be treated essentially like a big floppy drive. That is, you can literally drag and drop files to it, use the copy command to copy files onto the disc, and so on. The packet-writing software and UDF file system manage everything. If the disc you are using for packet writing is a CD-R, every time a file is overwritten or deleted, the file seems to disappear, but you don't get the space back on the disc. Instead, the file system simply forgets about the file. If the disc is a CD-RW, the space is indeed reclaimed and the disc won't be full until you literally have more than the limit of active files stored there.

Unfortunately, Windows versions up through Windows XP don't support packet writing or the UDF file system directly, so drivers must be loaded to read packet-written discs and a packet-writing application must be used to write them. Fortunately, though, these typically are included with CD-RW drives. One of the most popular packet-writing programs is DirectCD from Roxio. You can even download a universal UDF reader application from Roxio for free that enables you to read UDF 1.5 (packet-written) discs on any CD-ROM or CD-RW drive.

When you remove a packet-written disc from the drive, the packet-writing software first asks whether you want the files to be visible to normal CD-ROM drives. If you do then the session must be closed. Even if the session is closed, you can still write more to the disc later, but there is an overhead of wasted space every time you close a session. If you are going to read the disc in a CD-RW drive, you don't have to close the session because it will be capable of reading the files even if the session isn't closed.

A newer standard called Mount Rainier adds even more capability to packet writing and is one of the most important developments in CD and DVD drives. With Mount Rainier, packet writing can become an official part of the operating system and the drives can support the defect management necessary to make them usable as removable storage in the real world.

Photo CD

First announced back in 1990 but not available until 1992, Photo CD is a standard for CD-R discs and drives to store photos. The current version 1.0 of the Photo CD standard was published in December 1994. You simply drop off a roll of film at a participating Kodak developer, and they digitize and store the photos on a specially formatted CD-R disc called a Photo CD, which you can then read on virtually any CD-ROM drive connected to a PC running the appropriate software. Originally, Kodak sold Photo CD "players" designed to display the photos to a connected TV, but these have since been dropped in favor of simply using a PC with software to decode and display the photos.

Perhaps the main benefit Photo CD has brought to the table is that it was the first CD format to use the Orange Book Part II (CD-R) specification with multisession recordings. Additionally, the data is recorded in CD-ROM XA Mode 2, Form 2 sectors so more photo information could be stored on the disc.

Using the Photo CD software, you can view your photographs at any one of several resolutions and manipulate them using standard graphics software packages.

When you drop off your roll of film, the Kodak developers produce prints as they normally do. After prints are made, they scan the prints with ultra-high-resolution scanners. To give you an idea of the amount of information each scan carries, one color photograph can take 15MB20MB of storage. The compressed, stored images are then encoded onto special writable CDs, and the finished product is packaged and shipped back to your local developer for pickup. Some developers can do the scanning onsite.

Photo CD Disc Types

The images on the disc are compressed and stored using Kodak's own PhotoYCC encoding format, which includes up to six resolutions for each image, as shown in the table below. Kodak has defined several types of Photo CDs to accommodate the needs of various types of users. The Photo CD Master disc is the standard consumer format and contains up to 100 photos in all the resolutions shown in the table except for base x64.

The various resolutions supply you with images appropriate for various applications. If, for example, you wanted to include a Photo CD image on a web page, you would choose a low-resolution image. A professional photographer shooting photos for a print ad would want to use the highest resolution possible.

The Pro Photo CD Master disc is intended for professional photographers using larger film formats, such as 70mm, 120mm, or 4"x5". This type of disc adds an even higher-resolution image (4,096x6,144 pixels) to those already furnished on the Photo CD Master disc. Because of this added high-resolution image, this type of disc can hold anywhere from 25 to 100 images, depending on the film format.

The Photo CD Portfolio disc is designed for interactive presentations that include sound and other multimedia content. The high-resolution images that take up the most space are not necessary here, so this type of disc can contain up to 700 images, depending on how much other content is included.

Multisession Photo CDs

One breakthrough of the Photo CD concept is that each of the disc types is capable of containing multiple sessions. Because the average consumer wouldn't usually have enough film processed to fill an entire disc, you can bring back your partially filled CDs each time you have more film to develop. A new session can then be added to your existing CD until the entire disc is filled. You pay less for the processing because a new CD is not necessary, and all your images are stored on a smaller number of discs.

Any XA-compliant or XA-ready CD-ROM drive can read the multiple sessions on a Photo CD disc, and even if your drive is not multisession capable, it can still read the first session on the disc. If this is the case, you must purchase a new disc for each batch of film you process, but you can still take advantage of Photo CD technology.

Kodak provides software that enables you to view the Photo CD images on your PC and licenses a Photo CD import filter to the manufacturers of many desktop publishing, image-editing, and paint programs. Therefore, you can modify your Photo CD images using a program such as Adobe Photoshop and integrate them into documents for printing or electronic publication with a page layout program such as Adobe PageMaker.

Picture CD

Although Kodak still offers Photo CD services, the high cost has led to limited popularity. Kodak now offers the simpler Picture CD service. Unlike Photo CD, Picture CD uses the industry-standard JPEG file format. It uses a CD-R, with up to 40 images stored at a single medium-resolution scan of 1,024x1,536 pixels. This resolution is adequate for 4"x6" and 5"x7" prints. The images can also be made available via Kodak PhotoNet, where the same images are posted online and can be downloaded. In addition, Kodak has a service called Picture Disk that stores up to 28 images on a 1.44MB floppy disk at a resolution of 400x600, suitable for screensavers and slide shows.

The software provided with Picture CD enables the user to manipulate images with various automatic or semiautomatic operations, but unlike Photo CD, the standard JPEG (JPG) file format used for storage enables any popular image-editing program to work with the images without conversion. Although the image quality of Picture CD isn't as high as with Photo CD, the much lower price of the service should make it far more popular with amateur photographers. Services similar to Picture CD are also offered by Fujifilm and Agfa, and some stores allow you to order Kodak Picture CD with your choice of store-brand or Kodak film processing.

White Book Video CD

The White Book was introduced in 1993 by Philips, JVC, Matsushita, and Sony. It is based on the Green Book (CD-i) and CD-ROM XA standards and allows for storing up to 74 minutes of MPEG-1 video and ADPCM digital audio data on a single disc. The latest version (2.0) was released in April 1995. Video CD 2.0 supports MPEG-1 compression with a 1.15Mbps bit rate. The screen resolution is 352x240 for NTSC format and 352x288 for European PAL format. In addition, it supports Dolby Pro Logiccompatible stereo sound.

You can think of video CDs as a sort of poor man's DVD format, although the picture and sound quality can actually be quite goodcertainly better than VHS or most other videotape formats. You can play video CDs on virtually any PC with a CD-ROM drive using the free Windows Media Player (other media player applications can be used as well). They also can be played on most DVD players and even some game consoles, such as the Playstation (with the correct options). Video CDs are an especially big hit with people who travel with laptop computers, and the prerecorded discs are much cheaper than DVDmany cost as little as $5.

Super Video CD

The Super Video CD specification 1.0, published in May 1999, is an enhanced version of the the White Book Video CD specification. It uses MPEG-2 compression, an NTSC screen resolution of 480x480, and a PAL screen resolution of 480x576; it also supports MPEG-2 5.1 surround sound and multiple languages.

Most home DVD-creation programs can create Video CDs or Super Video CDs.

Blue Book CD EXTRA

Manufacturers of CD-DA media were looking for a standard method to combine both music and data on a single CD. The intention was for a user to be able to play only the audio tracks in a standard audio CD player while remaining unaware of the data track. However, a user with a PC or dedicated combination audio/data player could access both the audio and data tracks on the same disc.

The fundamental problem with nonstandard mixed-mode CDs is that if or when an audio player tries to play the data track, the result is static that could conceivably damage speakers and possibly hearing if the volume level has been turned up. Various manufacturers originally addressed this problem in different ways, resulting in a number of confusing methods for creating these types of discs, some of which still allowed the data tracks to be accidentally "played" on an audio player. In 1995, Philips and Sony developed the CD EXTRA specification, as defined in the Blue Book standard. CDs conforming to this specification usually are referred to as CD EXTRA (formerly called CD Plus or CD Enhanced Music) discs and use the multisession technology defined in the CD-ROM XA standard to separate the audio and data tracks. These are a form of stamped multisession disc. The audio portion of the disc can consist of up to 98 standard Red Book audio tracks, whereas the data track typically is composed of XA Mode 2 sectors and can contain video, song lyrics, still images, or other multimedia content. Such discs can be identified by the CD EXTRA logo, which is the standard CD-DA logo with a plus sign to the right. Often the logo or markings on the disc package are overlooked or somewhat obscure, and you might not know that an audio CD contains this extra data until you play it in a CD-ROM drive.

A CD EXTRA disc normally contains two sessions. Because audio CD players are only single-session capable, they play only the audio session and ignore the additional session containing the data. A CD-ROM drive in a PC, however, can see both sessions on the disc and access both the audio and data tracks.

Purple Book

The Purple Book defines the standards for double-density CD-ROM (DDCD), CD-R (DDCD-R), and CD-RW (DDCD-RW) media and drives. It was announced by Sony and Philips in July 2000, and the current 1.0 standard was released in July 2001.

Purple Bookcompliant rewritable drives can read and write standard CD, CD-R, and CD-RW media and achieve their higher 1.3GB (versus 650MB for standard drives) by modifying the following features of existing CD-ROM, CD-R, and CD-RW standards:

• The track pitch has been reduced from 1.6 micrometers to 1.1 micrometers, and the minimum pit length has been reduced from 0.833 micrometers to 0.623 micrometers to enable double-density recording.

• CIRC7, instead of regular CIRC, error correction is used.

• An expanded ATIP address format is used.

DD drives support digital rights management. They are designed to prevent the creation of DD music CDs. The tables below provide the details of the sector format used by DD drives

Although DDCD drives have twice the capacity of traditional drives, very few of them were sold. Sony offered several models in 2001 but has since discontinued them, although DDCD media is still available.