CD-ROM has been the primary delivery system for such high-volume content as databases and multimedia by virtue of its 680MB capacity. Not only has CD-ROM evolved into many related formats, but a totally new format, DVD, is on the horizon. Is the CD-ROM obsolete? This paper investigates the CD-ROM's past, present and future to answer this question and many more.
Various CD standards have been published in the form of "color" books; for example, the original audio CD's standards are called the Red Book. Other "color" books will be described in this paper in the descriptions of the formats they define. Also included will be some lesser-known proprietary formats that have either come and gone for one reason or another, or have survived to fill some niche. But all share the same silvered polycarbonate makeup, and together they tell a story of both success and failure.
CD audio (CD-DA) – Red Book
As previously mentioned, the original CD audio specifications are called the Red Book. The original compact disc (magnetic disks are spelled with a "k", while optical discs are spelled with a "c") was only intended to be a common delivery medium for a single kind of content – music. This music, digitized at 44.1KHz with a range of 16 bits, or over 65,000 possible values, has been available since 1980 when Compact Disc-Digital Audio, or CD-DA, was defined by Philips N.V. and Sony Corporation. An interesting fact about CD-Audio is that its data is stored in a manner that allows recovery from scratches. Instead of being arranged in distinct physical units, one frame is "interleaved" with many others so that a scratch or other defect will not destroy a single frame beyond its ability to be corrected. Instead, a scratch will destroy a small portion of many frames, which can all be recovered.
Since the Red Book came first, it is the basis for all other types of compact disc. All other members of the CD family either include or refer to the specs of the Red Book. Offshoots of the Red Book evolved to enable different types to data to be added to the content.
With one such offspring, CD+G, the "G" stands for graphics, albeit elementary and sluggish in performance, so users have something to look at while the music plays.
CD Text, as the name implies, allows textual data such as song titles, lyrics, fan club information, and the like to be available along with the music. Both are combined in a CD+G Text application. All these formats, however, require players that can retrieve and display the additional information on a TV screen.
Enhanced CD, which comes in an assortment of types known, among others, as Mixed-mode, Hidden Track, and CD Extra or CD Plus, are all attempts to develop a disc that plays music on an audio player, and CD-ROM-like content such as video, text, still images, etc. on a computer.
CD-ROM – Yellow Book
The Yellow Book CD-ROM specification, announced by Philips and Sony in 1983, includes two data structures: Mode 1 and Mode 2.
Mode 1 defines CD-ROM data with ECC (Error Correction Code) and is used when data integrity and safety are of the utmost importance, like databases or programs. Mode 2 has no ECC, providing a bit more room for data. It is normally used in situations where data error is less critical, like video, audio, or graphic images.
The vast majority of CD-ROMs produced are Yellow Book, Mode 1 for Windows or DOS. These discs can be accessed by Macintosh or UNIX-based computers, but they don't behave like "native" Apple or UNIX discs. Even so, the plain vanilla CD-ROM is the single most standardized medium for data storage ever produced.
Multimedia-type CD-ROM offerings are the most common Mode 2 creations. Some of these are CD-ROM/XA; so-called bridge discs such as Photo CD, Karaoke CD, and Video CD; and CD-i, or Green Book (further described below). Besides Mode 2, all these formats have something else in common: they are all intended to play on specialized consumer electronics playback devices. Some, like Video CD and Photo CD, will also play on a computer.
Another specification defining a CD-ROM standard is known as ISO 9660, which was developed by an ad hoc committee called the High Sierra Group. This group came together to eliminate the early practice of each CD-ROM publisher using a different, incompatible CD-ROM file format. Extensions to this standard were developed to allow CD-ROM applications to operate on multiple platforms while retaining their "native" operability on their own platforms.
Another cross-platform CD-ROM alternative is a hybrid disc, which contains multiple partitions formatted for different operating systems, and that are only detected by the proper platform.
CD-i – Green Book
CD-i stands for Compact Disc Interactive. It is unique in the CD family in that it is the only specification which defines not only the disc and the contents, but an entire hardware and software system. Its primary uses are in kiosks, training, and mobile interactive sales presentations. It is especially practical for presenting high-capacity interactive multimedia to computer novices. A CD-i player connects to a stereo system and TV set. Photo CDs can also be played in a CD-i player, as well as in a conventional CD-ROM drive.
Video CD – White Book
Video CD is a Mode 2 White Book specification allowing up to 74 minutes of VHS-quality, full-screen video. It can be played in a computer's CD-ROM drive, but the computer must have an add-in MPEG (a compression format developed by the Motion Picture Experts Group) video card. It can also be played on a CD-i player, but the player must have an add-on cartridge. There are also dedicated Video CD players. Although Video CD is not particularly popular in the US or Europe, it is all the rage in Asia, where there is virtually no installed base of inexpensive VCRs and thus very little competition. Because of Video CD's ability to deliver great-looking video but inability to hold an entire full-length movie, efforts to develop a new, high-density, high-capacity video disc for the consumer market were increased. White Book got its start from the Karaoke CD format, which is very popular in Japan.
CD-R – Orange Book Part II
Orange Book Part II defines CD-R, or Compact Disc Recordable. This was a major breakthrough for the CD-ROM format, because for the first time CD-ROMs could be created in a desktop setting. The first recordable CDs could only be recorded on once, whether it was 68 bytes or 680MB. However, soon multi-session recording was introduced, allowing subsequent data to appended to already-recorded data. This is what really launched CD-R's rise to current popularity. One drawback, however, is that in order to circumvent the stamped-at-once original nature of CD-ROM, each separate recording session exacts a toll of up to 15MB of overhead. CD-R recorders have plummeted in price as they have been widely adopted, and it has been predicted that before long most computers will come with them preinstalled instead of ordinary CD-ROM drives, boosting their popularity even further.
CD-RW – Orange Book Part III
CD-RW stands for CD-Rewritable, which some say will be the last stop on the CD development trail. The Orange Book Part III definition was released by – you guessed it – Philips and Sony in 1994. This may at first seem like the ultimate convenience – creating CD-ROMs, only to erase them and record again. However, there is a major obstacle. The laser optics necessary to perform this miracle make CD-RW discs incompatible with existing CD-ROM drives, unlike CD-R discs, which are fully compatible. However, CD-RW will probably succeed, not because of its incompatibility with the past, but because of its compatibility with the future. The reason is that the phase-change technology inherent in CD-RW is also present in DVD, so that future DVD drives will most likely be able to read CD-RW discs. But here's where incompatibility comes in again, because DVD drives will not be able to read CD-ROM and CD-R discs unless they are equipped with a second laser just for that purpose. Sony has produced a dual-laser drive already, and other manufacturers are working on similar devices.
DVD
Speaking of DVD, what exactly is it? It is the blending of two initially competitive technologies. The first originated in January, 1993 when Nimbus Technology and Engineering of Gwent, Wales demonstrated a double-density Red Book CD-Audio disc containing two hours of MPEG 1 video at a trade show. The Red Book standard was chosen because at the time there was no other choice – Video CD had not yet been introduced and conventional CD-ROM specifications, because of the high overhead inherent in error correction, severely restricted the playback speed and capacity of the video data.
The second competitive technology to spawn DVD was a demonstration of Optical Disc Corporation's double-density White Book-format Video CD in October, 1993, again at a trade show. These innovations proved to be a source of embarrassment for Philips and Sony, who were the former innovators but who now had been beaten to the punch regarding the introduction of a CD able to contain and play back two hours of video on existing platforms.
By December of 1994 Philips and Sony unveiled their proposed high-density format, which they called MMCD. The following month an alliance of companies initiated by Toshiba and Time Warner announced support for a competing format called SD, for Super Density disc. Each competing side in this war tried to enlist various companies to side with them. Eventually, however, they agreed to combine the best features of each format to create a solution acceptable to both the computer and entertainment industries. The result was DVD, which originally stood for Digital Video Disc, then Digital Versatile Disc, and now just DVD. It was thought that this was finally the universal medium that would forever eliminate the incompatibilities and cross-platform problems that plagued the CD format before it. The expectation was that a single DVD disc could be played in a music player, a video player, a computer, or a game device, which would unite the computer market with the consumer electronics market.
This optimistic view took into account the data itself, but not the ways humans control and use it. The result is that there are now three read-only DVD formats in the works: one for video, one for audio, and one for computer data.
DVD-R
Recordable DVD, or DVD-R, may follow much more closely on the heels of read-only DVD, or DVD-ROM than CD-R followed CD-ROM, which took eight years. In fact, the time frame may be only a matter of months. Pioneer DVD-R drives and media were scheduled to be available in June or July of this year. The proposed capacity of these discs is 3.9GB, which could be doubled by using two-sided discs. The first generation of these drives will have something in common with its ancestor, the original CD-R drives, in that only one session can be recorded, called Disc-At-Once.
DVD-RAM
Rewritable DVDs have been dubbed DVD-RAM, and their introduction will again burst the bubble of universal compatibility. Although there are no definite standards yet, the companies working on them have confirmed that the first generation of 2.6GB DVD-RAM discs will not be readable in regular DVD drives. Other proposed formats would yield from 3GB to 5.2GB. No one is sure when DVD-RAM will become a reality.
DVD is the new format of the present and the definite format of the near future. But just as compact discs evolved far beyond what they were originally intended to do, its inventors can only hope that DVD, if necessary, will be adapted as well. Who knows what modifications future file formats, operating systems, and hardware innovations will require, and if DVD will be the long-term answer. What was hoped to be the universal medium for delivery of all digital information has already been split into three separate formats optimized for video, audio, and computer data. But the interesting factor is that even with the advent of the mighty DVD, the ancient CD-ROM is not altogether obsolete, simply because of the huge installed base of CD-ROM drives, the lower price of CD-R recorders and media, and the wide acceptance of the familiar CD format. In short, the announcement of the death of CD-ROM is still somewhat premature.
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