I recently wrote a post called Backing Up Digital Photos where I outlined the various backup media you can use. I discussed the advantages and disadvantages of the various media. After the post I decided to talk more about the longevity of a CD/DVD, since that is probably the most used media for backups.
Parts of a CD-R
Before discussing how long a CD-R will last, it is important to discuss what a CD-R is made of. The most obvious component of a CD-R is the clear plastic disk, which is usually made from some kind of polycarbonate.
The reflective part of the CD-R comes from a metal foil that is glued to one side of the polycarbonate. A protective paper or plastic label will usually cover the foil in the expensive CD-R, while the foil may be the top portion of the CD-R for lower cost brands. This foil can come in many colours, but silver (aluminum) or gold are the most common.
The data on the CD-R is stored on a dye that is between the upper surface of the polycarbonate and the reflective metal foil. When data is recorded, the laser beam goes through the polycarbonate and melts a small pit into the dye. The laser turns on and off very rapidly, which results in melted and unmelted areas. These areas represent the ones and zeroes of the data.
Now that you have an understanding of what comprises a CD-R, you may be wondering what this has to due with its longevity? The next section will discuss that.
CD-R Longevity
The reflective colour of a CD-R is determined by two things: the metal foil and the dye used. The type of material used can affect how long a CD-R will last. Although the oxidization of aluminum can affect the data, it is very rare that it happens. The gold foil does not oxidize as easily so it really has no impact on the data.
The biggest impact on the longevity of a CD is the type of dye that is used. There are a few main dyes used in CD-Rs: cyanine, phthalocyanine, and metallized AZO. Each dye has a different chemical composition, so their colour and shelf-life are different. The following table outlines the different dyes.
| Name | Colour | Shelf Life |
|---|---|---|
| Cyanine | Blue, Blue-Green | 10 years |
| Phthalocyanine | Light Aqua | 100+ years | Metallized | Dark Blue | 50-100 years |
Long Lasting Products
There are many CD-R products produced by a few companies that can probably last a long time without any issues. The most popular, and probably the most expensive, are the Taiyo Yuden CDs and DVDs. Brands such as TDK and Verbatim are said to carry the Taiyo Yuden brand.
Another popular long-lasting brand of CDs and DVDs is the MAM-A brand from Mitsui. According to the Web site, the shelf life of a CD-R disc is 329 years, while 116 years for the life of a DVD-R disc.
There is some debate as to what brand is better, but for what it’s worth, I think you can’t go wrong with either. The way technology is progressing, any CD or DVD you burn today probably won’t be used in 100 years, or possibly 10 years for that matter. You will constantly be upgrading your backup technology to keep pace with the industry.