Ad Terras Per Aspera

(Last updated July 26th 2009)

Ahh, I’ve been planning to write this one for awhile: an entire article on archival quality media. As I do professional software development as well as professional photography (what a weird combination), I need archival quality CD and DVD media to store my data on.

However, one of the hardest things to is actually find good media, or even understand why it is good media. This article focuses on the history of Compact Discs, writable CD/DVD media, and why DVD+R is superior to DVD-R. If you want to just know what media is worth buying, skip to the summary at the bottom.

Short history of the Compact Disc
The invention of the Compact Disc has had a large impact on both music and computing in the last 20 years. Invented in 1979 as a joint project between Sony and Phillips to counter the self-destructive nature of consumer audio playback (such as tapes and records that could only be played so many times before the recording degraded significantly) by switching to a resilient digital format.

The CD was also designed to store standard computer data, as in 1985 the first CD drives for computers were released; massive, bulky, and expensive, it was not until the mid-90s that they really took off, driven almost solely by video games and large multimedia applications.

In 1990, Sony and Phillips went back to the drawing table, and then came out with the CD-R, a record-once medium. Yet again, the first CD burners were large, expensive, and bulky, but by the late 90s having a CD burner was the new ‘in’.

The first few generations of CD media, designed by Taiyo Yuden (a company who I respect, and buy all my archival quality media from), actually kind of sucked; it wasn’t until around 2000 that companies started producing very high end media.

CDs and DVDs store individual bits (encoded in various ways depending on the media) with spots of reflective and non-reflective areas. This method is called ‘pits and lands’, where pits ‘absorb’ light (ie, are ‘off’ bits) and lands ‘reflect’ light (ie, are ‘on’ bits).

With pressed media, the pressing method causes pits to reflect the laser’s light away from the sensor, and the lands to reflect it back at the sensor. With burned media, a high energy laser causes spots of organic dye to go opaque and obscure the reflective surface for the pits, leaving the organic dye for lands alone.

Short history of the DVD
While burning was becoming popular in the late 90s, so was playing high quality video on DVDs. Storing almost 7 times the data of a 700MB CD (or almost 13 in the case of dual layer DVDs), allowed companies to store massive amounts of data on one disc, leading to the movie industry to drop VHS tapes and the video game industry to drop CDs.

In 1995, the first DVD specification was ratified by over a dozen companies including Sony and Phillips, as well as Thompson, Pioneer, and Mitsubishi. By 2000, at least half the homes in the US and Japan had DVD players.

So, obviously, the next step was to produce burnable DVDs. Two separate, and incompatible, efforts took hold. The first one, Pioneer’s DVD-R (pronounced ‘DVD dash R’) was released in 1997, using different data storage methods than pressed DVDs (appearing to be more like CD-R than DVD), a poor error correction scheme, and the ‘wobble’ laser tracking system of DVD-R is inadequate for the job.

The second effort, lead by the DVD+RW Alliance (headed by Sony, Phillips, Mitsubishi, and Thompson) was released in 2002, as an alternative to the poorly implemented DVD-R. DVD+R uses a superior ‘wobble’ laser tracking system, a far better error correction method, and the media quality itself is typically higher. (See the ‘Why DVD+R?’ section below for a more technical explanation)

Why archival media is hard to produce
Unlike pressed CDs/DVDs, ‘burnt’ CDs/DVDs can eventually ‘fade’, due to five things that effect the quality of CD media: Sealing method, reflective layer, organic dye makeup, where it was manufactured, and your storage practices (please keep all media out of direct sunlight, in a nice cool dry dark place, in acid-free plastic containers; this will triple the lifetime of any media).

The silver and aluminum alloys used in virtually all blank CD/DVD media has one major issue, requiring the manufacturer to lacquer a protective seal over the entire disc: silver and aluminum oxidize when they hit air, turning the normally reflective layer into silver or aluminum rust. Some (very expensive) media uses gold instead which doesn’t oxidize, however DVD media cannot use gold due to design issues (not true anymore, see update below). Today, only the cheapest of the cheap media has severe issues with sealing practices (as such, avoid any media made outside of Japan and Taiwan; especially avoid media made in India).

Assuming that the protective seal and reflective layer are manufactured correctly, the next issue is the organic dye. The first organic dyes, designed by Taiyo Yuden, were Cyanine-based and, under normal conditions, had a shelf life of around ten years; simply, that was simply unacceptable for archive discs. Taiyo Yuden, Mitsubishi Chemicals, Mitsui Co., and Ciba Specialty Chemicals spent the next ten years trying to produce the best organic dyes, eventually reaching archive-quality CD media.

Taiyo Yuden produced ‘Super Cyanine’, a chemically stabilized version of the original Cyanine dye designs, while TDK offers media that uses ‘metal-stabilized Cyanine’ dye, leading to similar shelf lives as Taiyo Yuden’s media. Taiyo Yuden states their Super Cyanine dye is chemically stable for at least 70 years, and TDK states their metal-stabilized Cyanine is also stable for 70 years.

On the other hand, Mitsubishi went in a different direction and produced what is called a Metal Azo dye, that they claim is stable for around 100 years. Azo dyes are chemically stable, however, the shelf life of media using Azo dyes typically does not exceed that of Super Cyanine and metal-stabilized Cyanine.

The third dye produced for CD media is called Phthalocyanine dye, with the majority of such dyes produced by Mitsui and Ciba. Typically marketed as more resistant to heat and UV radiation than Cyanine and Azo, modern Cyanine and Azo dyes last just as long in extreme conditions.

DVDs also use similar dyes, however manufacturers have intentionally kept what dyes they use a secret (instead of a feature in their marketing of the media), and all blank DVDs are intentionally the same color (as different dyes on CDs make blanks different colors, however, it is not indicative of what dye is used due to some manufacturers using different colored silver alloys and non-reactive additives in the dye).

Why Taiyo Yuden media, and how to buy in the US
The best discs in circulation tend to be Taiyo Yuden media, which you rarely can buy directly. In Japan, you find their media under the brand That’s, which are wholly owned by Taiyo Yuden. In other countries, popular brands such as TDK and Verbatim carry their media (see the Taiyo Yuden FAQ by the CD Freaks Forum for a listing).

Simply put, I have never had problems with any kind of Taiyo Yuden media. Ever. I have bought CDs and DVDs under a dozen different brands (including non-Taiyo Yuden manufactured TDK and Verbatim), and the only ones that have had a 100% success rate is Taiyo Yuden.

If you cannot find any company selling Taiyo Yuden under the own brand, I suggest buying from the SuperMediaStore.com, who offer a wide range of Taiyo Yuden CD media, DVD-R media, and DVD+R media. I tend to buy just from them, as they are the only company that guarantees that their media is actually from Taiyo Yuden and not a fake (see the above linked FAQ on information about fake Taiyo Yuden media).

Why DVD+R?
This is the most technical section of the article. If you don’t understand the basics of how CD/DVD media works, or find such technical discussions boring, skip to the next section.

As I said earlier, DVD-R sucks for data preservation for three reasons: inferior error correction, inferior ‘wobble’ tracking, and the fact its data writing methods look like an un-needed halfway point between CD-R and DVD+R. The wobble tracking I shall explain first, then the error corrections method, then the specifics of ATIP/pre-pit/ADIP optimum power settings.

For a CD/DVD burner to track where it is on the disc, it uses three things: the ‘wobble’ of the data track (where it actually wobbles back and forth instead of in a straight line) to tell where it is in the track, the position of the track to tell where it is on the disc, and some additional information on the disc to tell where the track (singular, as CDs and DVDs only have one track, and it is written in a concentric spiral) begins and ends.

This additional information on a CD-R is called the ATIP (Absolute Time In Pregroove), which contains how long the track is, where it begins, what the maximum and minimum writing speeds are, what formula dye it uses, who actually made it, optimum power control settings, and error correction data. The ATIP is stored as a frequency modulation in the wobble itself.

However, since the wobble changes subtly to encode data, it is impossible to use with the small size of tracks DVD requires, as electric noise in the laser pickup and wobbles introduced by the electric motor spinning the disc, these could easily be read as frequency changes in the real track itself.

On DVD-R, they tried to solve the problem with something called ‘pre-pits’ where spikes in the amplitude of the wobble appear due to pits fully out of phase with the rest of the track (ie, between two spirals of the track, where there is no data). This can be viewed as a simple improvement over CD-R as it makes it easier to track the wobble (since the wobble is constant except for the easy to detect and remove spikes).

Unfortunately, this method as one flaw: due to electric noise in the laser pickup, it would be very easy to miss the pre-pit (or read one that wasn’t actually there) if the disc were damaged or spun at fast speeds. The time to read a pre-pit is 1T (roughly .0000000038th of a second), which even for a computer can be easy to miss. DVD-R traded hard to track frequency changes for hard to read wobble-encoded data.

On a DVD+R, however, they came up with a much better method. Instead of changing the frequency of the wobble, or causing amplitude spikes in the wobble, they use complete phase changes. Where CD-R’s and DVD-R’s methods make you choose between either easy wobble tracking or easy ATIP reading, DVD+R’s method makes it very easy to track the wobble, and also very easy to encode data into the wobble. DVD+R’s method is called ADIP (ADdress In Pre-groove), which uses a phase change method.

With ADIPs’ phase changes, the direction of the wobble changes and continues on going in the exact opposite direction (ie, counter-clockwise to clockwise, or the reverse). For example, if the wobble was ‘going up’, the phase change causes it to instantly reverse direction start ‘going down’ no matter where it in the wobble cycle. The phase change is very easy to detect, and also continues for a set period (in this case, one 32T section of the track, or 32 times longer than the pre-pit method of DVD-R).

The state of the phase change (clockwise or counter-clockwise) encodes the individual bits in each block In essence, with the phase change method, not only do you have an easy way of tracking the wobble, but you now have an easy way of reading wobble-encoded data.

As I mentioned earlier, this wobble-encoded data includes error correction of wobble-encoded data itself. Error correction is the most important part of media, because if it does not work, then you’ve lost your data, even if there is nothing seriously wrong with the disc.

The DVD-R specification states that for every 192 bits, 64 of them are not protected under any scheme, 24 of them are protected by 24 bits of parity, and the last 56 bits are protected by another 24 bits of parity. This weird (to put it mildly) scheme allows you to easily scramble or lose 25% of the data that is required to read your disk! This information is almost more important than the actual data burned on the disc itself.

The DVD+R specification, however, states that for every 204 bits of information, it is split into four blocks of 52 bits containing 1 sync bit to prevent misreading because of phase changes, 31 bits of data, and a 20 bit parity (that protects all 32 bits of data). The sync bit is always the same value in all four blocks, and exists only to prevent phase inversions.

Now, the third item on the list: how DVD+R discs burn better. As I said earlier, ATIP/pre-pit/ADIP stores information about optimum power control settings. This information is basically formulas stating how much output power is needed, what the laser startup power should be, and other pieces of information you require to properly burn a DVD.

Optimum power control output is dependent on three things: burning speed, laser wavelength, and information given to the drive about the media. DVD-R basically fails on all three accounts because DVD+R simply includes far more information about the media in the ADIP data than DVD-R does in it’s pre-pit data.

DVD+R includes four optimum profiles, one for four major burning speeds (usually 2x, 4x, 6x, and 8x, though this can change as speeds increase). Each of these profiles include optimum power output based on laser wavelength, more precise laser power settings, and other additional information. With this information, any DVD+R burner can far more optimize it’s burning strategy to fit the media than it can with DVD-R, consistently providing better burns.

For comparison, DVD-R includes one profile, optimum power output based for that one profile only and uncalibrated towards what wavelength it is for, less precise laser power settings, and no other additional information. Typically, DVD-R burners have to already know how to burn a certain piece of media (and include this information in their firmwares) before they can properly burn to it. New media often is not properly supported.

In addition to the optimum power control profiles, DVD+R also gives four times more scratch space for the drive to calibrate the laser on; more space can only improve the calibration quality. So, in short, DVD+R media exists to simply produce better burns and protect your data better.

And finally, the end of the article…
Finally, after roughly three pages of technical discussion, we arrive at the end of my dissertation on archival quality CD/DVD media. So, you’re probably now wondering, in simple terms, what media do I recommend?

To begin with, I do not recommend CD-RW, DVD-RW, or DVD+RW media in any form for permanent storage. This is mostly a no-brainer, but those discs are meant to be able to be changed after burning, and they are simply unsuitable for long-term archival storage. I also do not recommend DVD-R media due to DVD+R’s superior error correction and burning control.

That said, I recommend Taiyo Yuden media across the board. Taiyo Yuden currently manufactures 52x CD-R, 16x DVD-R, and 8x DVD+R media in normal shiney silver, inkjet printable, and thermal printable forms. Taiyo Yuden may be one of the most expensive (if not the most expensive), but their media quality is unsurpassed. Taiyo Yuden (currently) does not produce any dual layer media. Also, as I mentioned earlier, I recommended buying from SuperMediaStore.com as they are the only online US distributor that guarauntees that their Taiyo Yuden media is certified as coming from Taiyo Yuden.

However, for those that absolutely require dual layer media, Verbatim produces DVD-R DL and DVD+R DL, however, due to the fact DL media costs over twice as much as two single layer discs, I recommend you only use single layer unless you really, really need a single disc.

So, what am I using? Due to Taiyo Yuden’s superior media quality, and DVD+R’s superior design, I use only Taiyo Yuden DVD+R media. I recommend this media to everyone who wishes to keep their data for a long, long time.

Update: It seems MAM-A and Kodak actually has managed to make a gold DVD, though no one else seems to be manufacturing them. However, MAM-A’s gold archival media still doesn’t seem to exceed TY quality (although Mr 60,000 in the comments below puts TY second best to MAM-A). Due to the extreme cost of gold archival media ($2+ a disc) with very little increased protection (if any), I’ll still say TY media is better. I want to see more independent tests on this before I change my recommendation.

In addition, I’d like to mention that Verbatim has been relabeling other brands of disc as their own. If the box/spindle/cakebox the discs come in don’t say they’re manufactured with Verbatim’s proprietary Azo dye (sometimes called Advanced Azo, sometimes not, depending on the product) then they aren’t Verbatim media at all and should be avoided as they may not meet typical home archival standards.

Update 2: (Sept. 19th 2007) Its almost been a year since I first wrote this article. My recommendations for media have not changed, my recommendations for DVD burners have.

Plextor: I once owned a Plextor PX-716, and it was a great drive, considered by many to be one of the best drives ever manufactured. At one point I had recommended in this article that if you could find one it was worth buying, but they are rare and slow compared to modern Samsung drives..

Samsung: Samsung is currently producing two drives worth owning, the
Samsung SH-S223B (SATA) and the Samsung SH-S222A (IDE). These drives have a large fanbase over at the CD Freaks forums, and seem to be a good buy since Plextor is no longer in the loop.

Update 3: (July 26th 2009) Its been awhile since I updated this article. Pioneer is no longer manufacturing drives worth using. Just buy a Samsung drive like I link to above. I’m using two Samsung drives now after my PX-716 finally died after years of service.

My recommendation on TY and Verbatim hasn’t changed, and I imagine it will never change; DVD media will not change significantly from here on out. Bluray in my opinion is not worth switching over to unless you’re storing data that can be measured in terabytes.

When Bluray is worth switching over to, I’ll write a follow up article to this one. High quality single layer media will have to drop below 50 cents a piece and Bluray burners will have to become ubiquitous (much like DVD burners are now) before that happens. I’m thinking 2010 or later.