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A Few Facts About Recordable CD ROMs
Just a few more facts about the recordable CD.
There are basically TWO types of CD-Rs on the market --- the standard computer CD and the "music" CD. The music CD costs more because of a special royalty paid to the music publishers. Since they have a special feature on each music CD that home music stereo recorders look for, no other CD will record in these music machines. These music CD-Rs also use a protection system that prevents you from making a copy.
Another type of recordable CD is the CD-RW (read/write). It is basically a CD-R with re-writing capabilities for a thousand or more times. This one is not discussed in this article.
The STANDARD computer CD-R can record music using a computer and can, additionally, record computer files such as MP3 or photo files. Generally, in this article we'll assume the use of a standard computer type CD-R. These are now commonly inexpensive and in some promotional programs FREE.
Several dye colors are used for the layer where burning takes place. Either an aluminum or gold reflective layer is used for the reflective surface. One report claims the "best" seem to be those that have the blue dye on the gold reflective layer. The combination of the blue dye on the gold makes the disc appear green.
The life of a CD-R, where data can be reliably read, is in the range of 75 to 100 years. While experts aren't in agreement, a CD begins to degrade sometime between 35 and 100 years, but "remain usable for much longer." Compare this to digital audio tape with a life expectancy from 10 to 20 years. Being realistic, though, your ancestors will be asking, "CD? What's a CD? Never heard of them!" With the way technology is being improved our present day CD will be like the old 78 rpm records in just a few short years.
You may find your own experimentation and selection of brand and combination best. Over time, the manufacturing and processes used will change -- hopefully, always for the better.
Do NOT use a slow speed CD-Rs in a CD recorder that records at a higher speed than the CD-R can handle.
The recordable CDs are more fragile than the stamped commercial ones. Labels, for instance, must be the low adhesive type, otherwise they will "lift off" or damage the recording surface of the disc. NEVER remove a stick-on label once applied. The most fragile part of a CD is immediately under that LABLE !!! A scratch on this surface can permanently damage the CD.
I prefer to eliminate the stick-on lable by directly writing onto the CD-R. When doing this DO use a soft, felt-tipped type marker such as a "Sharpie." This will assure that you don't accidentally dig into that fragile recording surface which is immediately under that writing area.
Keep them away from heat, direct sun, and high humidity. Since it is a DYE on that disc, high heat, humidity, and sun can destry this layer. On the other hand they are not destroyed by magnetic fields.
One recordable CD ROM contains the equivalent of seven Zip disks, 473 3.5" diskettes or the equivalent of 400,000 pages of ASCI text printed on 20 lb. paper (this would be a stack of paper about 65 feet high).
What this REALLY means is once you've filed it away on the disc you may be forever looking for that file again unless you get some reliable file system organized. =:0
So how is a typical recordable CD-R made? The reflective gold or aluminum discs are formed of a layer of clear polyurethane, a translucent layer of photosensitive dye, a very thin layer of gold or aluminum to act as a reflector. Then, finally, on the top, a thin protective over-coating is applied to act as additional protection when writing on the disc surface. So, the written information is really immediately under that label area! Scratches on the label side are far more destructive than those on the bottom, clear plastic surface.
A CD-ROM reader works by shooting a weak laser beam through the clear polyurethane to the dye and reflective layers. This reflective surface reflects the laser beam back to a sensor. Depending upon the opaqueness of the dye layer, the reflected beam comes back either strong or weak .... thus allowing a read of the data on the CD.
Information is stored on a CD-R disc when your CD recorder "burns" the CD-R. The infra-red diode is brought up to a high power where it can change the dye from clear to opaque, as needed, to record the data.
The CD-R machine is an electronic marvel. Motors pull the disc into place. Another motor positions the head at the proper location on the disc surface. A third motor spins the CD at a very precise speed. Additionally, the infra-red laser diode has a focus assembly which consists of electro-magnets to rapidly and constantly assure the beam is precisely focused on the moving recording surface of the disc.
For more extensive information on recordable CDs, click here
This page updated: June 15, 2002