The Digital Dark Age


Yesterday my 13-years old daughter called me for help because her laptop hard disk was rather full. It was a matter of minutes to realize that most of her storage (i.e. 90%) was filled by images, audio and video files. In fact, she has a camera and she likes to take lots of snapshots of her friends. Since her digital camera allows her to take short videos too, at least 40% of her hard disk was stuffed by AVI files. She also ripped most of my audio CD’s to MP3 — that’s legal, don’t worry — and saved them in her laptop so that she could hear her favorite music while surfing the web. Like me, she likes Queen and RHCP.

"Well, you have to move at least the biggest files on removable media, if you wish to free some space", I told her.

"Ok, dad. But where? Should I move them on a CD, a DVD, or an external hard disk?"

"Does it make any difference?", I asked her.

"I do not know. How long does a CD last?"

"Well, it depends on the media quality. Soon or later, all CD’s will degrade."

"Hey, am I going to loose all my stuff in few years? What’s about an external hard disk?"

"Well, probably the most reliable solution nowadays could be to store in the web."

"But that’s private stuff! I don’t want to share’em!"

Well, to make it brief I promised her to work on it. Probably, as a medium term solution, I will suggest her to move most of her stuff to an external hard disk and then to backup the saved files on few DVD’s too. However that discussion made me think. So I did some researches, and here is the outcome.

Optical disks

Usually, in a pressed optical disk (CD’s and DVD’s) data are literally molded into the media and will not disappear unless the disk is physically damaged. This is not true for recordable optical disks. In fact recordable optical disks use dyes that change reflectivity or color when heated, as well as various types of reflective coating layers. There are many dye types and they do not all have the same stability. Same for coating: any type has a different life expectancy. Four basic chemical formulae are used for the recording layer dye, that is:

  1. cyaninelight green or blue in color
       low cost to make, most common and lowest permanence;
  2. phthalocyaninetransparent with a slight green tint
       highest permanence and second most common;
  3. metalized azoblue
       similar in quality to phthalocyanine, costs less to make and is not common;
  4. formazanlight green
       a combination of cyanine and phthalocyanine, similar in quality to phthalocyanine but costs less to make, and is not as common.

Notice that some manufacturers may modify one of these dyes to create a custom proprietary formula and change the traditional color of the dye. So, do not rely on color to identify the dye. As far as reflective coating is concerned, there are several types too:

  1. aluminium alloy
      the poorest, since it corrodes when exposed to oxygen;
  2. silver alloy
      better than aluminium, but it corrodes when exposed to sulfides in air;
  3. pure silver
      good, even if it may also oxidize in air;
  4. pure gold
      the best, in absolute.

Notice that good coating does not imply good dye too. Furthermore, some manufacturers place a gold-color label on the non-read side, or add a funky gold-color layer on the read side. Do not rely on those disks. In general, it is not easy to know if a disk is high-quality by simply observing it.

Last, but not least, to avoid to expose the reflective coating to air, optical disks are lacquered. High-quality manufacturers make it nice and thick or will even apply a separate protective coating. A thin lacquer may expose the disk to oxidation if the protective coating or lacquer is scratched. Bulk disks are usually low-quality: they have thin lacquer, aluminium alloy reflective coating, and cyanine dye. They are good to transfer files from a PC to another or for temporary storage, but do not rely on them to preserve data on the long term.

So, how long does an optical disk last? The answer is surprising: a low-quality disk may last no more than two years, whereas a high-quality one may last up to 200 years! Of course, it also depends on how you take care of your disks. Exposure to direct light and to extreme levels of temperature and humidity may significantly decrease the life expectancy, especially if you damage the disk surface. In any case, quality makes the difference!

Hard disks

Two years ago I tried to revive my old Amiga 3000. So I pulled all parts out of the box, I connected the monitor, the mouse, and the keyboard, inserted the Kickstart disk into the drive, and switched on the computer. It worked. Everything, but… the hard disk: the heads were probably glued to the magnetic surfaces of the rotating platters. There was no way to save it. By the way, all 3"½ diskette were still readable.

So, hard disks die too. Of course the Amiga 3000 drive died because I did not use it for years and probably I did not protect it in the most appropriate way, but in any case the failure rate of any hard disk increases with the age of the drive. Once the failure rate goes beyond a certain threshold, you cannot rely anymore on it. The failure rate also depends on many other factors, as usage, temperature, electrical shocks. It is not easy to make a forecast, of course. For example, Google made an analysis and the result was that the probability of failure due to high usage of their disks increases significantly after four years.

Manufacturers sometimes measure the life expectancy of hard disk by using a number called Mean Time Between Failures (MTBF). This number significantly varies from one thousand to one million hours in some case. To translate MTBF in something that is meaningful to end users is not so easy. Generally speaking, people want to know what percentage of drives they can expect to fail at a given time. Of course, the quality of the drive and the operating conditions count also for hard disks as well as for optical ones. The computer itself has a lot to do with the life of the hard drive inside. So the average life of an hard disk can be 2 up to 20 years, but soon or later it will die too.

The Web

When you store data on the web you do not know and do not care how they will be preserved. Someone else will take care of your data, will protect them, will backup them. Probably. Of course, it depends on the service provider. You may expect that paid services be better than free ones, but this in not necessarily true. In many cases free services are based on business strategies which guarantee that your data will be safe for a long, long time. At least, if the service provider will survive in a very competitive marketplace! But what if it goes bankrupt? What if the service is no more profitable? You are without certainties in those cases too. So the web is not necessarily the solution.


Probably, nowadays, the best approach would be to store your files on an external hard disk, backup the hard disk on high-quality optical disks in a compressed format, and to save the backup on some fee-paying hosting system. Your data will probably last at least for your lifetime.

But… what will happen next? "Who care?", you may say. Well, what about your children? And what about your grandchildren? Today I can still watch at photographs of my great-grandfather. They are not perfect, some are scratched, some are faded, but I still have them. I do not need any specific tool to look at them. Several years ago, during a genealogical research, I read a parchment written by an ancestor of mine on 1456. The ink was faded but still readable, and even if my Latin is not so good, I could read what he wrote about six centuries ago! And of course, archeologists can read documents written several thousand years ago on paper, parchment, papyrus, wax, wood, and stone. Our history is mostly written on medium which were intended to survive for centuries, and they did. But what about digital content?

As I said in the previous sections, most media designed to store digital data may last from few years to few centuries. Of course, if someone will take care to continuously move those data from old media to new ones, maybe they could last for millennia, but who will take care of my daughter’s files? Her children? Her grandchildren? Maybe, but what about formats and devices? Nowadays I cannot read anymore the data I stored on old 5"¼ floppy disks. Even I would find a 5"¼ floppy driver, I should use the same program that was used to write those data to read them, but most of those programs do not exist anymore. By the way, even if I would find some copies, they might not run on modern operating systems, especially if they were created on extinct platforms like Quantum Leap, Atari, Commodore 64, Amiga 1000, Apple ][, and so forth. Furthermore, many formats were proprietary too, so that modern applications might not import those files anymore.

The conclusion is really sad and worrying: we live in the era of information, but it is very probable that most pieces of information we are creating will not be preserved for future generations. Maybe, in 2786 AD, a future archeologist will be probably still able to read the Dead Sea scrolls, but he will not be able to read anymore my daughter’s movies and photographs. Of course, you may think that teen’s files cannot be compared to ancient important manuscripts, but most of archeological finds are objects for everyday use. So, are we risking to become a new Dark Age for future historians?

Commenti (2) a «The Digital Dark Age»

  1. utente anonimo ha detto:

    Nice story, the life of a medium seems becoming shorter and shorter and not only because if the physical characteristics. I mused about that on my article Technological updates and the right to silence

    Ivo Quartiroli

  2. utente anonimo ha detto:

    Parchment Bookmarks

    [..] Bookmarked your page with keywords parchment! [..]

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