11.9 Media Issues
There's been a lot of nonsense written about CD-R media. One person swears that gold/green discs are great and silver/blue discs worthless, and another says the opposite. The truth is that there are distinct differences in media, but no absolutes. Disc A may work perfectly in Drive A and not work at all in Drive B, and Disc B may work perfectly in Drive B and not at all in Drive A. That situation is less common with recent drives than it was with older models, but some drives still show a strong preference or dislike for particular disc types.
In general, newer drives, name-brand models, and those with current firmware are unlikely to have problems writing almost any brand of disc, except perhaps those you find on sale in the bargain bin. Older drives, no-name models, and those with outdated firmware may be very choosy indeed about which discs they'll use. Discs differ as follows.
CD-R blanks use one of these reflective layers:
- Gold
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The metal used in early CD-R discs, and still used in some current discs. The advantage of gold is that it is stable. The disadvantage is that gold is expensive, even in the microscopically thin layers used in CD-R discs. As the price of CD-R discs plummeted, the cost of gold became an increasingly large part of the cost of the disc, which led some makers to substitute silver. By early 2002 many disc manufacturers had discontinued gold-based products or limited gold reflective layers to their premium or "professional" lines. Note that some CD-R discs that appear gold in fact use little or no gold in their formulations.
- Silver alloy
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The advantages of silver alloy relative to gold are that it is relatively inexpensive and actually has better reflective characteristics across a wide spectrum. The chief disadvantage of silver is that it corrodes. Even a tiny crack in the label layer can allow airborne pollutants, particularly sulfur dioxide, to gain access to and react with the silver layer. If this occurs, the CD becomes unreadable.
Most current CD-R blanks use one of these dyes (although to avoid patent infringement, some disc manufacturers use similar but not identical dyes):
- Cyanine
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As the name indicates, this dye is cyan (bluish-green) in color. Used with a gold reflective layer, cyanine-based discs appear green on the clear side and gold on the label side (the so-called "green/gold" discs). Used with a silver reflective layer, cyanine discs appear light blue/silver. Cyanine was the first dye used to make CD-R discs, and quickly developed a reputation for stability problems. That has been overcome in current discs by using metal-stabilized cyanine. The advantage of cyanine is that it is more sensitive to light than other dyes, which means that cyanine discs tolerate a wider range of LASER power settings, making them more likely to be compatible with any given drive and firmware revision. For example, a typical cyanine disc can be written with a LASER power setting between 5.5 and 7.5 milliwatts, while a typical pthalocyanine disc requires 5.0 to 6.0 milliwatts. On the downside, accelerated aging tests show expected lifetimes for cyanine-based discs of "only" 50 years or so, significantly less than other dyes. In practical terms, no one 50 years from now will have a drive capable of reading any CD, so this matters little.
- Pthalocyanine
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This dye is a very pale yellow-green color, approaching colorless. With a gold reflective layer, discs appear gold/gold or greenish-gold/gold. With a silver layer, they appear light yellow-green/silver or even silver/silver. Because cyanine-based CD-R discs were protected by patent, other manufacturers developed alternative dyes, including pthalocyanine. The one thing to be said in favor of pthalocyanine is that its lower light sensitivity relative to cyanine gives it estimated archival stability of nearly 100 years. Lower light sensitivity also means that pthalocyanine-based CD-R discs are less likely to be compatible with any given CD-R drive, particularly an older model. All recent CD-R drives support pthalocyanine-based discs, and most older models can accommodate them with a firmware upgrade.
- Azo
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This dye from Mitsubishi Chemical is a deep blue color. Azo discs use a silver reflective layer, which gives the data side a very deep blue color. Azo is even less sensitive to light than pthalocyanine, which gives azo-based discs expected archival stability of more than 100 years, and makes drive support even more problematic than with pthalocyanine. All recent CD-R drives support azo-based discs, and most older models can accommodate them with a firmware upgrade. Due to their insensitivity, some early azo-based discs did not support writing faster than 1X or 2X, but current azo-based discs such as the Verbatim Super Azo discs can be written at 48X or faster.
There is no single answer to the question, "Which is best?" There are numerous variables in the CD-R manufacturing process. The thickness and density of the dye layer vary, as does that of the reflective layer. Some manufacturers have begun using dyes that resemble those listed earlier, but have different characteristics. There is no way to tell by appearance alone which dye a disc uses. The physical groove structure of different CD-R blanks may differ, to optimize that disc for different LASER powers, writing speeds, and schemes. But the bottom line is that all CD-R blanks, including the no-name ones, are much better than they were a few years ago. The primary measure of CD-R disc quality, Block Error Rate (BLER), is much lower now than in the past. Even an average disc made in 2003 is as good or better than the best discs made a few years ago.
In the past, the problem was that, although most CD-R disc manufacturers made every effort to comply with strict Orange Book specifications, some CD writer manufacturers did not. The upshot was that different writers varied widely in which discs they could use successfully. In general, more compromises were made with inexpensive writers, which were typically much more media-sensitive than were more expensive models. A $175 Plextor burner would probably work with just about any media you chose. A $75 no-name ATAPI burner might have been very choosy indeed about which blanks it was willing to write.
Fortunately, those days are gone. Most current CD writers, even $50 ATAPI models, provide excellent compatibility with a wide range of disc blanks. Even so, it's important to keep your drive firmware up to date. As disc manufacturers change formulations and new disc types come on the market, you may need to update your firmware to enable your drive to use those new blanks.
When choosing discs, your sole criterion should be which media work properly in your recorder. The best starting point is one of the disc brands recommended by the drive manufacturer. Most manufacturers provide such a list on their web sites. Those lists are updated as new media types become available, and assume you have the latest firmware. At the price of blank CDs nowadays, there's little point to using bargain brands. We buy 48X-certified Taiyo Yuden blanks on spindles of 100 for something like $0.30 per disc and use them in all our burners. There's simply no point to risk using no-name blanks to save a few cents each.
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11.9.1 Writable CD Capacities
Standard CD-R discs are available in 63-, 74-, and 80-minute lengths, which respectively store about 550, 650, and 700 MB of data in ISO-9660 format. For example, a nominal 74-minute CD-R disc stores (74 min x 60 sec/min x 150 KB/sec) = 681,984,000 bytes, 666,000 KB, or 650.390625 MB. CD data formats use 2 KB sectors, which means that a standard 74-minute disc contains (666,000 KB / 2 KB) = 333,000 sectors. Most blanks actually contain more than the required number of sectors. For example, a nominal 74-minute blank may contain 344,250 sectors, which translates to 76.5 minutes. This "extra" space permits overburning (writing more data to a disc than its nominal capacity) if the CD writer and software both support overburning.
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Remember that when you write data to a CD recorder, the 2 KB logical sectors are actually written to 2,352 byte physical sectors, with the remaining space used for ECC code. That means that a standard 74-minute CD-R blank actually stores (333,000 sectors x 2,352 bytes/sector) = 783,216,000 bytes or about 747 MB. Accordingly, you may find 74-minute discs with identical true capacities advertised as having nominal capacity from 650 to 780 MB, although something in the 650 to 680 MB range is most common.
When selecting CD-R discs, use the lowest-capacity discs big enough for your data. In practical terms, that means using 74-minute CD-R blanks rather than 80-minute blanks whenever possible. The 63-minute blanks have now all but disappeared from the market, and even the 74-minute blanks are becoming an endangered species. That's a pity because few burned CDs contain more than 63 minutes (550 MB), and CDs recorded on 63-minute blanks are in every respect superior to those recorded on 74-minute or 80-minute blanks. They are more likely to be readable on more CD-ROM drives and CD players, and are less likely to generate read errors. However, 63-minute blanks fell prey to the pervasive "more is better" way of thinking. Most people, given the choice of a 63- or 74-minute blank for the same price, chose the latter. The 63-minute blanks became harder and harder to find, and their increasingly limited distribution meant they eventually cost more than 74-minute blanks, and so disappeared from the retail channels. Alas.
You may not have the choice of 74- versus 80-minute blanks, depending on your CD writer. Not all CD writers can use 80-minute blanks, and even if the drive supports 80-minute blanks, your CD burning software may not.
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Before DVD writers became a mainstream technology, several manufacturers tried and failed to introduce higher-capacity replacements for CD-R. Most of these efforts were trial balloons that promised capacities of 1 GB to 1.5 GB, but disappeared without a trace before drives actually shipped. One exception was the Sony Spressa CRX200E-A1 Double Density drive, which shipped in limited numbers in 2001. This drive stored 1.3 GB on a CD-like disc, but had a fatal flaw. It required special double-density discs, which never achieved wide distribution, could not be used to record CD-Audio, and were incompatible with the Rainbow Book standards. Sony formalized its Double Density CD standard as the Purple Book, but that "standard" never caught on. Sony Double Density discs are now difficult to find.
Plextor took a different approach with the April 2003 introduction of PlexWriter Premium drives with GigaRec technology, which increases the storage capacity of standard CD-R discs by as much as 40%. Unlike earlier proposals to expand CD capacity, Plextor's solution is backward-compatible with existing drives and players. Although Plextor does not guarantee compatibility with every CD/DVD drive or player ever made?how could it??discs recorded with GigaRec can be read by most CD-ROM, CD-R/RW, and DVD-ROM drives and players. Some old, low-quality, or inexpensive drives may generate read errors with GigaRec discs, but those errors are attributable to drive deficiencies rather than to the GigaRec disc.
Although we have not yet put a PlexWriter Premium drive through our usual rigorous testing, we expect that its ability to store about 1 GB on a 700 MB CD-R disc will appeal to those who want an economical backup solution. Security-conscious people will also like PlexWriter Premium drives because they can burn password-protected discs.
11.9.2 Archival Stability of CD-R(W) Media
So how long can you expect that CD-R disc you just burned to last? There's been a lot of nonsense written on that topic, but ultimately the answer is that no one knows. Projected lifetimes of 50, 100, and even 200 years are casually tossed around, as though they had any meaning.
Here's the truth. The only way to know for sure if a disc will last 100 years is to burn one, wait 100 years, and try to read it. Obviously, that's not a practical solution, so media manufacturers use various testing methods to estimate archival stability. All of those testing methods depend on accelerated aging, achieved by storing the disc at temperatures much higher than normal, often in conjunction with high humidity and high ultraviolet flux intended to simulate bright sunlight.
The rule of thumb in chemistry class says that the rate of most chemical reactions approximately doubles for each 10º C (18º F) increase in temperature. So, in theory, if one assumes that normal storage temperature for a CD-R disc is 20º C, a disc stored at 30º C ages twice as fast as normal, one stored at 40º C ages four times as fast, one stored at 50º C ages eight times as fast, and so on. The trouble is that that rule of thumb is just that?a rule of thumb?and the reaction rate slope is linear over only a limited range of temperatures.
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So manufacturers project CD-R disc lifetimes based on testing them at high temperatures and in bright sunlight. But all that really determines is how long that CD-R disc is likely to last when stored at high temperatures in bright sunlight. Most people, of course, store their CD-R discs at room temperature and in the dark, or nearly so.
The real issue is not the archival stability of media, but the future availability of drives that can read the discs you're currently writing. Any CD you write today on a good-quality blank is almost certain to last at least 20 years, if not 100. But fast-forward to the year 2013. Finding a drive that can read a CD written in 2003 won't be a problem. In 2023, it may be a bit harder, but you should be able to find a drive that can read that CD written way back in 2003. But in 2103? Good luck. Try finding a drive today that can play back a wax cylinder audio recording made in 1900. Finding a drive to play a 100-year-old CD won't be any easier.
11.9.3 Labeling CD-R(W) Media
Finally, a few words about labeling. Drive and media manufacturers vary in what they recommend, and the best course is to follow those recommendations. However, some guidelines are nearly universal:
Never use a standard sticky label on a CD-R disc. The adhesive may damage the label side of the disc, causing it to degenerate rapidly and become unreadable. Also, the small weight of that label is sufficient to imbalance the disc in high-speed players. At best, such an imbalance may cause read errors. At worst, it may destroy the disc or even the drive.
The circular labels designed for CD-Rs are generally safe, but even they have been known to imbalance a disc if not applied perfectly centered. If you use such labels, never attempt to peel one off. Doing so may cause the top layer of the CD-R to separate, destroying the disc.
Do not use a hard-tip marker, which may score the label layer. We usually label CD-R discs with a Sharpie soft-tip permanent marker. Some sources recommend not using a permanent solvent-based pen because it may etch the label layer. Other sources, including some CD-R manufacturers, recommend using a solvent-based permanent marker. Although we've never had a problem using the Sharpie, for maximum safety choose your marker according to the recommendations of the disc manufacturer.
When hand-labeling is not neat enough?e.g., for discs you plan to distribute outside your company?consider using printable discs, which have a surface that may be printed with an inkjet and/or thermal printer. These are available in various types and background colors, and generally work well if you follow the manufacturers' instructions carefully. Until recently, only expensive special printers could print on CDs. In June 2003, Epson began shipping the Stylus Photo 900, a sub-$200 inkjet printer that the Stylus Photo 900 even has a separate CD tray that feeds CDS automatically to the printer, so you don't have to feed them manually one-by-one. Although we have not yet had an opportunity to test this printer, it is reported to work well with printable CDs. We expect other printer manufacturers to follow Epson's lead, so the era of ugly, hand-labeled CDs and DVDs may be drawing to a close.
