CD-ROM
By E.J. (Jerry) McFaul

First of all, what exactly is CD-ROM? Well, the acronym stands 
for Compact Disc - Read Only Memory. The compact disc portion of 
the name is probably familiar to you (certainly to your kids) as 
the highly successful medium that is now bringing music of 
incredible fidelity into our homes. Indeed, the compact disc is 
the most successful consumer product, as measured by total sales 
over time, ever introduced in the United States. The 
characteristic which accounts for its highly accurate 
reproduction of sound is the fact that the music is stored in 
digital form. Every second of music is equivalent to 
approximately 170,000 bytes of information, or about half of a 
standard 5 1/4 inch floppy disk. Therefore, in order to 
accommodate 60 or 70 minutes worth of music, the designers of 
compact disc technology (originally N.V. Philips, later Sony) had 
to provide for the storage of between 550 and 650 million bytes 
of information on a plastic disc only 4.78 inches in diameter. 
They accomplished this amazing feat by packing the bytes very 
close together along a continuous three-mile-long spiral track 
that is only one micron or 1/25,000 of an inch wide. These bytes 
are read by a highly-focused laser beam at a rate of 170,000 per 
second and transformed from a digital stream of ones and zeros 
into an audio waveform by a set of electronic chips inside the CD 
player. At the same time, a sophisticated optical-electronic 
servo mechanism constantly keeps the laser beam focused directly 
on the center of the spiral track, while elaborate error 
detection and correction circuitry ensures that less than one bit 
in a million is ever lost. And the most amazing thing of all is 
that this entire mechanism is able to flawlessly function inside 
of a device that can be bought in discount stores for as low as 
$79.95!

The reason for delving a bit into the world of audio compact 
discs (aside from the pure fascination with technology itself) is 
to provide a basis for understanding the closely related 
technology of CD-ROM. It wasn't long after the advent of the 
audio compact disc that some astute observer recognized that 
those same 550 to 650 million bytes that were being used to store 
Beethoven's Ninth Symphony could just as easily contain a 
complete bookshelf worth of printed material. Not only that, but 
the fact that all of the information was truly digital (just as 
the bytes of information on a floppy or hard disk) meant that 
computer techniques such as rapid search and retrieval could be 
used to provide rapid access to any part of that bookshelf of 
information. But perhaps the most significant benefit of CD-ROM's 
close association with the CD audio lies in the standardization 
of the technology. CD audio and CD-ROM discs share the same 
physical characteristics and are both produced at the same 
mastering and replication facility according to an international 
set of standards known as the "Red and Yellow Books." In 
addition, CD-ROM is blessed with yet another level of 
standardization approved by the International Standards 
Organization (ISO 9660) which defines the "logical" structure of 
the disc to ensure compatibility and accessibility across a wide 
variety of computing platforms. 

Standards are absolutely imperative in the world of computers 
where technology is rapidly evolving. Therefore, when a 
technology comes along that has both physical and logical 
standardization, that technology takes on a special significance. 
In the case of CD-ROM, that significance equates to long-term use 
and applicability. Unlike other types of optical storage media 
such as WORM (Write Once, Read Many) and Magneto-Optical 
Erasable, CD-ROM is not dependent upon the proprietary hardware 
or software from any particular manufacturer. Therefore, CD-ROM 
discs are truly interchangeable and can be accessed using a 
reader from any of a dozen different manufacturers. These 
characteristics set CD-ROM apart from any other type of optical 
media and make it the only true means of electronic publishing 
for the foreseeable future.