Close your eyes and see them now,

some 21st century scenes,the walrus and technologist

talking of many things,

of RAM and ROM,

of discs and DAKs

and especially CDs.

OK, we're not Lewis Carroll. And, unlike our tech-talking offspring, we're not 21st century creatures either. We're still learning to love surround sound. But just around the corner is a home revolution that could dwarf the business computer revolution.

Soon we'll be able to sit at one console and connect with the world. At our fingertips we'll have access to huge volumes of knowledge and entertainment via radio, TV, home and commercial video, audio records, tapes, CDs, computer, modem, telephone, fax and more.

To hear, see or interact with anything at all, we'll just push a button. Our console will do the rest.

One of the breakthroughs that makes it possible is CD-ROM technology. It's also called optical technology because it uses laser lights.

CD-ROM stands for compact disc-read only memory. Audio CDs also are read-only, unlike audio tapes. Ordinary computer discs have read-write memory. A computer can write information onto those discs in the same digital language used by CD-ROMs.

CD-ROM is revolutionizing the amount of space information takes up. A single 4.7-inch plastic CD-ROM disc can now hold some 600 megabytes of information. That's roughly equivalent to 1,500 old floppy discs, 300,000 typewritten pages, 5,000 picture images, or 16 hours of sound. It's enough to hold the entire Encyclopedia Britannica, which you can now buy on a CD-ROM.

Now, CD-ROM is being used most in experimental publishing. Each disc's capacity and low finished cost makes it cheaper to produce than a paper book with the same amount of data.

Microsoft has several CD-ROM products, including $150 Microsoft Small Business Consultant, a huge collection of 220 government publications on all aspects of running a small business. The disc can be searched for key words just like any computerized database. You can even transfer paragraphs from these readings into most word processing documents.

CD-ROM's inventors thought of these discs as just safe devices for storing masses of information in small spaces. Once they were laser-written with data, information was guaranteed safe from erasure.

Computers are capable of understanding the data on CD-ROMs since it's digital, the on-off or 0-1 language they understand.

But today's common computer disc drives can't locate the data on CD-ROMs. For that, you need a drive "head" that contains a laser.

You can use the disc with most computers if you buy a CD-ROM drive for as little as $700. You have to add software that bridges CD-ROM formats to computer formats.

CD-ROM technology is closely related to CD audio and CD video (CDV). (More than 2,700 movie titles are available now for CDV players, which cost $800 to $1,300 but should plunge in price on volume sales as fans discover CDV's razor sharp image quality compared to videotape.)

All these discs are made of the same substance and are pressed with the same machines. In both, information is stored as a series of microscopic pits and `lands' or flat spaces. These pits and lands, collectively called bumps, are molded into the plastic of the disc while it's being molded.

To read the disc, a beam from a small laser illuminates the surface of the bumps. The beam is scattered by the pits and reflected by the lands, producing the 0-1 digital language. A photodiode (or `electric eye') in the same `head' that holds the laser source distinguishes between the zeroes and ones as the light bounces back.

A CD-ROM disc never touches the "head." The bumps are buried within the disc. No matter how many times a disc is read, the data on it can't be lost or physically changed unless the disc is scratched, melted or otherwise defaced.

Most of us are already familiar with audio CDs. The main difference between preparing that and a CD-ROM disc is in quality control. All but the biggest errors made in audio disc pressing are inaudible to listeners. Even slight errors in CD-ROM laser-cutting can cause big problems. So assembly-line standards are a great deal higher for CD-ROM.

Similarly, CD-ROM players require more error-detection circuitry than players designed just for audio CD.

Data storage engineers are in a race. Some are attempting to create regular computer discs that can be written on by customers, yet hold as much as CD-ROMs.

Others are racing to find a way you can economically write as well as read CD-ROM discs in your own office. In fact, they've been attempting that for as long as we can remember.

Right now, we're pretty much stuck with factory-written CD-ROMs. It may not be long before technology provides affordable do-it-yourself data-etching machines. Soon after, by combining that with the sophisticated text and image scanners already available, we'll be able to convert our entire 5,000-volume library for storage in a square foot of space. We'll be able to catalogue the actual computerized images of Frank's entire output during 15 years as a photographer.

Our house will seem spacious again. But we probably won't notice it, since we'll be spending most of our time in front of that all-in-one audio-video-computer interaction center.

As a service to readers, the columnists answer questions and send a checklist of back issues if you enclose a stamped self-addressed envelope: TBC, 4343 W Beltline Hwy, Madison WI 53711. You can read back issues of this twice-weekly column at the electronic library, NewsNet, reachable via computer plus modem over phone lines. For NewsNet information, 800-345-1301. (C) 1989 P/K Associates, Inc.