The M-Disc - Durable but Possibly Doomed

How do they do it?

Commercially-produced, prerecorded CDs and DVDs are based on a series of pits (holes) and lands (not-holes) molded into the transparent polycarbonate lower layer of the disc. On top of that is a thin metal reflective layer. A laser shines through the bottom of the disk and the difference in reflectivity between the pits is read as data by the drive.

DVDs and CDs are both a kind optical discs, as the data are read optically, by a laser light.

The pits are in the top of the polycarbonate layer, which is itself topped by a shiny metal layer, to reflect the laser. There is a layer of lacquer to protect the shiny layer, and then (sometimes) artwork on the top.

Recordable discs have much the same construction, but instead of pits molded into the polycarbonate layer, there is a layer that contains a photosensitive dye, with the thin metal reflective layer on top. The laser writes to the disc by changing the color of the dye. The drive reads the difference in reflectivity of dye instead of pits.

The new M-Disc uses a laser to etch pits in the recordable layer, rather than by changing the color of a dye. Then the laser reads the difference in reflectivity of the media in the data layer. Perhaps (as the disc is backwards-compatible with standard DVD readers) there is a reflective layer on top of that - or the data layer is itself reflective. So as readable media, it is functioning very much like a manufactured music CD, with physical pits providing the difference in reflectivity when a laser shines on it.

The manufacturer claims that these discs will be readable for a thousand years, based on the expectation that the polycarbonate layer (the same polycarbonate layer shared by all CDs) ought to last a thousand years, but that the data layer, which they say is "rock-like" (but of secret composition) is permanent so long as it is protected by the polycarbonate layer. Hey, isn't metal kind of "stone-like."

But never mind - they go a step further, testing their media against other recordable media and coming out far in the lead. Noteworthy is the lack of a test against manufactured CDs.

How long do regular optical discs last?

Depending on the dye used, the shelf life of a recordable CD or DVD is generally quoted to be 10 to 100 years.

Kodak's testing says that "with 95% confidence, 95% of the population of KODAK Writable CD Media will have a data lifetime of greater than 217 years if stored in the dark at 25°C, 40% Relative Humidity after being recorded in a KODAK PCD Writer 200."

But said durability changes based on its exposure to heat, UV light, moisture and possibly other environmental considerations. As a result, although the media might be expected to last ten years (or 217) years, some portion of writable CDs fail after 3-5 years. Most manufacturers claim a shelf life of 5-10 years.

How long does a prerecorded CD last?

The Council on Library and Information Resources (CLIR.org), an interested party in the reliable storage of data, says that expectations vary from 20 to 100 years for these discs. They also say that there is a consensus among manufacturers writable CDs and DVDs,, CD-R, DVD-R, and DVD+R discs should have a life expectancy of 100 to 200 years or more under recommended storage conditions and rewritable (CD-RW, DVD-RW, DVD+RW, and DVD-RAM) discs should have a life expectancy of 25 years or more.

M-Disc claims a lifetime of 1,000 years.

Now, having data last for a thousand years (like books kept under the best conditions) is great. But what about the ability to read the discs in a thousand years?

CD-ROM readers started being popular around 1983. Although they were a bit expensive, they could hold around 700MB of data. About 5 years later, drives were released commercially that could write to recordable CD discs, and these drives became popular later in the 1990s. DVDs hit the market only around 1996 and could hold about 4.6 GB of data - more than six times as much data in the same space as a CD. In 1997 the DVD-R was released, allowing users to record their own DVDs. One I purchased in about the year 2000 cost me about $2000. As of the writing of this article (later 2011), such a drive is listed for about $40. A dual layer DVD that can hold twice as much as a standard DVD was made commercially available starting 2005 and a new double-layer DVD writer can be had today for about $50. Blu-Ray was released commercially in 2006, and a disc can hold 50GB of data and a Blu-Ray burner can be purchased today for about $120.

The moral of this part of the story is that formats change.

We are looking for ever-more, ever faster storage in ever-smaller, ever less-expensive forms of media. CDs were a dominant form of optical media storage for about 15 years - more or less the practical lifetime of the media. DVDs became the dominant optical media life form, but incompatible improvements happened inside of ten years. The DVD is looking to have a 15 or 20 year run - close enough to the expected lifetime of a disc. We've had Blu-Ray and double-layer DVDs for only a few years now and I would guess a phaseout in another ten years.

I myself am right now trying to unload a cabinet full of removable media drives. There are various optical, magneto-optical, tape and other removable magnetic media drives, such as Zip disk, Syquest and others. For more than a decade, I had offered a service of transferring data from one old format to something currently readable. Over the past five years, that part of my business has dropped away. I have tried to sell these drives on eBay, and to other vendors and there is no market for them. Only a specialized market exists and the vendors of such devices can't seem to unload them either. I can't give them away! Many of these are newer formats than CD and some are newer than DVD. At one time, some of these formats were near-standards and were ubiquitous as backup devices.

That Millenniata has created a form of writable media that they claim will last a thousand years is laudable. Their media surely seems to be more durable than other optical media. But what drives technology is (as I mentioned before) is ever-greater storage, ever-faster storage in ever-smaller, ever less-expensive forms of media. Millenniata is coming out of the gate with slower, more expensive media using (presumably) more expensive drives. if technology history is any guide, these drives and media will not become a standard and will have a much shorter than 15 year run. In something like ten years, these media may be just as easily viewable and readable as 8mm film is today. A hundred years from now, nobody will know what they are, much less a thousand.

With their great YouTube videos, and a logo I love, I believe these will make a small, short but exciting splash. It's great that they can hold up to being bashed on a table or dipped in liquid Nitrogen, but how many of us actually have this problem? The ExtremeTech website is certainly very excited about them "M-Disc is a DVD made out of stone that lasts 1,000 years" but in the end, draws a conclusion much like mine.

The M-Disc is a neat idea, but ultimately not much more useful than the faster, more capable media and technology already on the market for less. If this is their only product, the discs may be found intact hundreds of years from now, but I'm not so sure that the company will be.

Steve Burgess is a freelance technology writer, a practicing computer forensics specialist and expert witness as the principal of Burgess Forensics, and a contributor to the just released Scientific Evidence in Civil and Criminal Cases, 5th Edition by Moenssens, et al. Mr. Burgess may be reached at Burgess Consulting & Forensicshttp:// or via email at steve@burgessforensics.com

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