Genealogists love compact discs. Read any genealogy magazine or catalog, or visit a genealogy vendor’s Web site and you will find listing after listing for CDs. Large databases, out-of-print books, back issues of periodicals, images of census records&3151;the list goes on and on.
With the advent of CDs that you can write yourself, more genealogists are using this technology. We use them to share data and we use them to back up what we have spent countless hours creating, in case our hard drives crash. But are we getting the permanence that we think we are? There are several issues that need to be considered.
Definitions
With technology changing as it does, we must first review some definitions. CD-ROM stands for Compact Disc-Read Only Memory. It is what we usually think of when we think of a “CD.” The CDs that we buy that contain programs, databases, or music are CD-ROMs. They were written at a factory and cannot be changed by the consumer.
CD-R stands for Compact Disc-Recordable. It is different from a CD-ROM in that the consumer can create a disc, whether it is a back up copy of a hard drive, or a collection of images or databases. These CDs start out as blanks. The consumer can record on it one time (however, many CD-R drives will allow the user to record in several smaller segments, rather than requiring it to be all at one time). Once an area of the disc is recorded, it cannot be erased or changed.
CD-RW (Compact Disc-ReWritable) is the new kid on the block. Like a CD-R, a CD-RW (formerly known as CD-Erasable) allows users to record their own discs, but with a CD-RW users can also erase it and record again.
Another format in the world of CD technology is the DVD, which stands for either Digital Video Disc or Digital Versatile Disc, depending on who you ask. It is a relatively new technology that focuses on video. Because there have not been any real applications of DVD technology in genealogy (yet), this article will not delve into this area.
How CDs Are Made
CD-ROMs have different layers. Inside the disc is a layer of polycarbonate that is molded with pits. This layer is then coated with a reflecting layer of aluminum or a chrome-aluminum alloy. This reflective layer is what the laser beam inside the player uses to detect the pits. The reflective coating is then covered with another layer of plastic, then finally silk-screened with the label.
CD-Rs use a different method of storing the data. Instead of having pits stamped in the plastic, they use a layer of organic dye. As the laser in the recorder moves along, it darkens the dye from its original transparent state. When the laser in the player tracks through, the dye will affect how the reflective layer is read. Different manufacturers use different types of dye—including cyanine (which is green), phthalocyanine (which is gold) and azo (which is blue). To date, no studies have been found which indicate a significant difference in the type of dye used.
Instead of having a reflecting layer that cannot be changed, CD-RWs use an alloy which can change state when illuminated with a laser. Both types of writable discs have a groove stamped into the polycarbonate layer that allows the laser beam to track through the disc while being recorded or played.
Issues Affecting Physical Longevity
Because they are sturdier than floppy discs and magnetic tape, most people tend to think of CDs as inert objects. Barring scratches, they should last forever, right? Maybe not.
CD-ROMs made when the technology was new in the early 1980s had problems with the protective lacquer coating not fully covering the disc. Aluminum can easily oxidize and when the lacquer did not cover the entire disc, the oxidation would eventually cause the disc to be unusable (except as a coaster). The early CD-ROMs also were labeled with inks that eventually reacted with the aluminum, which also caused the discs to fail.
Fortunately, CD manufacturers realized what was happening and made changes in the manufacturing process to ensure better lacquer coverage, and stopped using chemically reactive dyes. (CD-Rs use metals such as gold that do not oxidize.) But there continue to be issues affecting the physical longevity of a CD.
According to the technical pages of several CD manufacturers and trade associations, estimates vary widely as to the expected longevity of the media:
- CD-ROMs are estimated to last anywhere from 30 to 200 years.
- CD-Rs, before they are recorded, have an estimated shelf life of five to ten years.
- CD-Rs, after recording, are estimated to last between 70 and 200 years.
- CD-RWs are expected to last at least 30 years.
Because CD technology is only about twenty years old (and recordable technology is younger than that), these expected life spans are estimates based on accelerated aging tests. As the testers at Kodak put it, chances are that if there is a significant error, the disc won’t work. Either it works or it doesn’t.
How the discs are handled and stored can greatly affect their longevity. CD-Rs, with their dye layer, are especially prone to light. Leaving them on a desk can lessen the dye’s reactivity when passed through the recorder’s laser beam. The dye’s chemical state also makes for the shorter life span before they are recorded. As time goes on, the dye loses its ability to change from transparent to opaque. In other words, if you are only going to use one every six months, do not buy the 50-pack at your local warehouse club.
CD-RWs have a similar problem with their alloy layer. After so many recordings and erasures, the alloy loses its ability to change from one state to another. This is estimated to occur around the 1,000th recording.
There are many things that the user does that can shorten a disc’s life. Fingerprints and scratches are the most common. It is especially important that writable CDs not have fingerprints on them before they are written, as the fingerprint can scatter the laser beam from the recorder or weaken the ability of it to change the dye or alloy. In this case, the data can be jumbled or not be recorded at all—both of which can result in an unusable disc.
Genealogists are becoming more aware of proper methods of writing on photographs and in scrapbooks, including using acid-free pens. The same advice should be heeded when labeling CDs. As noted previously, early CD-ROMs had inks in the labels that ate away at the disc. The same can happen if the user writes on a disc with a solvent-based marker. Water-based permanent markers are preferred. Ball-point pens should be avoided, as they can cause a scratch that shows through the reflective layer. For safest results, writing should be kept to the clear center portion of the disc.
Stickers should be used only with the greatest of care. Labels that are applied off-center or with air bubbles and creases can cause the disc to spin out-of-balance. This is especially harmful in high-speed recorders and readers. Removing a label can also damage the disc’s surface, rendering it useless.
Temperature can act upon the longevity of a CD. Several of the accelerated aging tests used 25ºC (77ºF) with 40 percent relative humidity as a baseline. Cooler, drier conditions should be beneficial. Conversely, warmer and damper conditions are a detriment.
Wide fluctuations in these conditions are harmful. These conditions can occur when you leave discs in the back seat of your car in July while you are reading a cemetery or in the trunk in the middle of winter when you are in the library.
Issues Affecting Software Longevity
So far, we have discussed several items that can affect the physical properties of a compact disc. There is another facet that must be considered—data on the disc.
Preferred formats change over time. Even though the disc may be in perfect condition, the data may be in a format that can no longer be read. An analogy is the collection of 78 RPM records that my husband inherited from his grandmother. They are in wonderful shape, but because the preferred format has changed (to CDs and audio cassettes), we cannot easily read the data (the music). A more recent example occurred in the 1970s and early 1980s with VCRs. Does the word “Betamax” mean anything to you?
Like 78s and Betamax tapes, computer formats change. Data have formats, written in a language that a computer can read. When the preferred format changes, it can be difficult to convert the data. Unlike 78s and Betas, sometimes it is more than a matter of finding the right machine to play it on. The issue is compatibility. Will the format that your data are in (GEDCOM, database, digital image, sound, etc.) be compatible with the format that is later preferred? In other words, what good is your CD if you have no way to read the data on it?
Software choices must be made with all due diligence and precaution. For the sake of the longevity of the data, it is better to use a database format that can be read over several different platforms. Having a proprietary format (one that can be read only with a special piece of software or hardware) is much more likely to cause problems with conversions later.
“But can’t we just convert the data when we want to change to a new and different format?” Maybe, maybe not. Data conversion is not a trivial matter and becomes trickier as the data become more complex. Think back to times when you have had to convert a document from one word processing program to another. Did all of the formatting convert correctly? Chances are that some of the formatting was lost—a tab here, a margin change there. The same is true for databases and other types of data.
Compounding the conversion issue is the concept of “backward compatibility.” This is used to describe the ability of a program to read earlier versions of itself. Most programs have this ability, at least to a degree. Problems can arise when the data are not converted on a timely basis. If too many newer versions of the program have been released, the most up-to-date version may not be compatible all the way back to the version in which your data are stored.
Summary
CDs have been a boon to the computing world, including the field of genealogy. They have enabled us to have large databases with complex search capabilities, easy back-up protection, and the ability to share large amounts of data and graphics with each other.
CDs, however, are not forever. They are dependent on aspects of their environment such as light and heat. Scratches and fingerprints also damage them. Care must also be taken to ensure that the data they hold are in a format that can be read and used.
With these caveats, genealogists and their CD collections should continue to grow for the foreseeable future—at least until the next medium of data storage comes along.
References
Amy Johnson Crow, CG is a professional genealogist who specializes in Ohio. She is a lecturer, past editor of the Ohio Civil War Genealogy Journal, recording secretary of the Ohio Genealogical Society, and chairperson of First Families of Ohio. A member of NGS, APG, and numerous state and county societies, she can be reached at amy@amyjohnsoncrow.com.
Genealogical Computing
