CD-Based Optical Technology

The first type of optical storage that became a widespread computing standard is the CD-ROM. CD-ROM, or compact disc read-only memory, is an optical read-only storage medium based on the original CD-DA (digital audio) format first developed for audio CDs.

Other formats, such as CD-R (CD-recordable) and CD-RW (CD-rewritable), are expanding the compact disc's capabilities by making it writable. As you will see later in this chapter, technologies such as DVD (digital versatile disc) enable you to store more data than ever on the same size disc.

CD-ROM drives have been considered standard equipment on most PCs for many years. The primary exceptions to this rule are thin clients—PCs intended for use only on networks and which normally lack drives of any type. CD-ROM discs are capable of holding up to 74 or 80 minutes of high-fidelity audio (depending on the disc used).

If used for data, the traditional 74-minute disc can hold up to 650MiB (or 682MB), whereas the newer 80-minute disc can hold up to 700MiB (or 737MB). A combination of music and data can be stored on one side (only the bottom is used) of a 120mm (4.72'') diameter, 1.2mm (0.047'') thick plastic disc.

CD-ROM has exactly the same form factor (physical shape and layout) of the familiar CD-DA audio compact disc and can, in fact, be inserted in a normal audio player. It usually isn't playable, though, because the player reads the subcode information for the track, which indicates that it is data and not audio.

If it could be played, the result would be noise—unless audio tracks precede the data on the CD-ROM. Accessing data from a CD-ROM using a computer is much faster than from a floppy disk but slower than a modern hard drive. The term CD-ROM refers to both the discs themselves and the drive that reads them.

Although only a few dozen CD-ROM discs, or titles, were published by 1988, currently hundreds of thousands of individual titles exist that contain data and programs ranging from worldwide agricultural statistics to preschool learning games.

Individual businesses, local and federal government offices, and large corporations also publish thousands of their own limited-use titles. As one example, the storage space and expense that so many business offices once dedicated to the maintenance of a telephone book library can now be replaced by two discs containing the telephone listings for the entire United States.

A Brief History

In 1979, the Philips and Sony corporations joined forces to co-produce the CD-DA (Compact Disc-Digital Audio) standard. Philips had already developed commercial laserdisc players, and Sony had a decade of digital recording research under its belt.

The two companies were poised for a battle—the introduction of potentially incompatible audio laser disc formats—when instead they came to terms on an agreement to formulate a single industry-standard digital audio technology.

Philips contributed most of the physical design, which was similar to the laserdisc format it had previously created with regards to using pits and lands on the disk that are read by a laser. Sony contributed the digital-to-analog circuitry, and especially the digital encoding and error-correction code designs.

In 1980, the companies announced the CD-DA standard, which has since been referred to as the Red Book format (so named because the cover of the published document was red). The Red Book included the specifications for recording, sampling, and—above all—the 120mm (4.72'') diameter physical format you live with today.

This size was chosen, legend has it, because it could contain all of Beethoven's approximately 70-minute Ninth Symphony without interruption. After the specification was set, both manufacturers were in a race to introduce the first commercially available CD audio drive.

Because of its greater experience with digital electronics, Sony won that race and beat Philips to market by one month, when on October 1, 1982 Sony introduced the CDP-101 player and the world's first commercial CD recording—Billy Joel's 52nd Street album.

The player was first introduced in Japan and then Europe; it wasn't available in the United States until early 1983. In 1984, Sony also introduced the first automobile and portable CD players.

Sony and Philips continued to collaborate on CD standards throughout the decade, and in 1984 they jointly released the Yellow Book CD-ROM standard. It turned the CD from a digital audio storage medium to one that could now store read-only data for use with a computer.

The Yellow Book used the same physical format as audio CDs but modified the decoding electronics to allow data to be stored reliably. In fact, all subsequent CD standards (usually referred to by their colored book binders) have referred back to the original Red Book standard for the physical parameters of the disc.

With the advent of the Yellow Book standard (CD-ROM), what originally was designed to hold a symphony could now be used to hold practically any type of information or software.