Science Questions

Will CDs be decodable in years to come?

Sun, 23rd Sep 2012

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Steve Caffyn asked:

Hi Dr Chris,


I am curious to know if the naked scientists think we would be able to read data information on a CD, DVD, or hard-disc etc if we had advanced technology but no historical records of the code or computer language the data is written in.


For example if our civilisation had some sort of EMP apocalypse and rendered all our electronics exposed to it useless, or our civilisation regressed and then advanced again but with slightly different technology, or an intelligent alien race found our data would they be able to even recognise it as data storage. With the advent of the electronic book I wonder if we'll lose everything if we don't just print it in a basic form that we can retrieve but also I guess I'm thinking about my backups generally, and redundancy in all kinds of file types!




PS love the podcasts!






Dave -   This is assuming that you’ve got the device, it’s still in perfectly working order and if you have the thing to read it, it would be perfectly fine, but would’ve lost all those - could you work out what was on it in the first place?  I think different ones have different difficulty.  Something like a CD, which is of course 1980s or 1970s technology, if you looked at it with an electron microscope, you'd see lots of little pits on it and if you can go through those pits, they represent lots of ones and noughts and there's not a lot of compression, certainly with an audio CD, and therefore, I would’ve thought that if you had some idea that there was some data on there and you had to look for it, if you are a bright bloke and you're the kind of person who hangs out in the computer science department, you'd be able to work out what was on it.  Whereas, if you're talking about something which was really heavily compressed like an mp3, then you're going to have to know more about how it was encoded to be able to decode it.  You don’t just have a series of numbers which indicate how loud the sound is.  So, you're going to have to work out a lot more.  I'm not saying that we couldn’t do it, but it will be a lot more hard work.


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Hitachi have announced a long life data storage system syhprum, Wed, 26th Sep 2012

Maybe if they know the aliens who've got the golden record and managed to work out the instructions on how to play it ...

RD, Thu, 27th Sep 2012

I'm  not sure that even without a major computer crash that our CD's will be readable in a century.

I'd be hard pressed to find a way to read an 8", 5¼", or even a 3½" floppy.  CDs are all but obsolete now.  Fortunately they are still more or less backwards compatible with the DVD and Blu-Ray devices.  But, what will the next rev bring?  Perhaps a move to all flash & PROM distribution media? 

I suppose given a circular disk shaped media, one would deduce that it would be played in a circle.  I haven't looked at one under a microscope, but perhaps the tracks, sectors, and even bytes would be obvious. 

Of course, dead languages are much more difficult to decipher without the Rosetta stone to guide one's way. CliffordK, Thu, 27th Sep 2012

Maybe the CDs will be used as lip plates  ...  RD, Fri, 28th Sep 2012

Assuming the aluminium layer hasn't been tarnished by moisture seeping in, then the data should still be there.
The question is whether people (smart technology people) could figure out the bit/encoding structure merely by analysing a collection of CDs.
I suspect it's do-able (though not at all easy) for CDs, as the format was devised in the very early 80's and won't be very complicated. That said, it still interleaves data and has error-checking codes built-in, which wouldn't be immediately obvious.

When it comes to the newer standards such as DVDs (with more powerful error-checking and correction) not to mention highly compressed data formats such as MPEG video and MP3 audio I think you'd be very unlikely to 'reverse-engineer' these and reconstruct the sound or movie without some prior knowledge or documentation of the file-formats.

(Edit to add: Ow - I didn't see Dave's answer before writing this, honest!) techmind, Fri, 28th Sep 2012

Surprisingly CD-R or CDRWs are actually not as stable as analog recordings. Be it photo, tape, record or printed paper the expected life of a CD-R is much less than analog media. Production CDs are more stable but can also be chemically degraded over time. Nothing within the CD would be affected by EMF radiation. It could however destroy the reading device by decoding the microchips. But if a EMF pulse destroyed all CD readers you could make another one from a paper schematic. If you did not have a paper copy you'd have to reinvent the CD reader/player but the media would not be changed.  BioChemSFC, Thu, 18th Oct 2012

Look back just a few decades to what was then the height of technology.

Recordings made on wax cylinders, 78 rmp records and the much newer 45 & 33 1/3 rmp records. Not knowing what they are or how they work, would you spin them around and stick a needle in them? If you answered 'yes' to that question, would you then do the same to a CD? Alternately, would you fire a laser at a wax cylinder? What of Betamax and now even VHS.

Look back further still, about 5 - 9,000 years back. We might still be puzzled by Egyptian hieroglyphs but for discovery of the Roseta Stone.

With hieroglyphics, we could at least read the data, evenif we could not understand it. With modern technology, its a case of reading it first, then translating it into something undestandable. Unless we ensure we leave a Roseta Stone equivalent and the means to access the data, all might be lost. Don_1, Tue, 15th Jan 2013

That could work ... RD, Tue, 15th Jan 2013

To the human eye, a DVD almost reflects white light - the slight rainbow tinges hint that there is a fine structure there, of roughly the same size as the wavelength of light, but the track structure would be hard to see before the development of the electron microscope, hard to read without a laser, and impossible to decode without powerful electronics. The intentional encryption applied to DVDs would add another layer of complexity.

The DVD is very much a product of our current level of technology, but probably decodeable by someone with a more advanced technology and lots of computing power - providing the information is still intact.

There is a principle in Information Theory that the better you encode some piece of information, the more indistinguishable it is from white noise - and white noise does not carry any information. This measure is called "Entropy" - and encryption maximises entropy.

See (a bit mathematical, unfortunately).
evan_au, Tue, 15th Jan 2013

If one of the paper copies of this survives it will help Bored chemist, Fri, 18th Jan 2013

I fixed your link.
It is a good point that one shouldn't have all copies of a specific technology based on that technology.

There are a lot of CD & DVD drives in the world today.  But, I find it amazing how quickly floppy drives all but vanished, and the optical disk formats (CD, DVD, Blu-Ray), are already showing signs of becoming obsolete, especially with laptop computers. CliffordK, Fri, 18th Jan 2013

I have CD'S bought in the 80's that are no longer playable,not due to over use or bad handling, but due to because the reflective layers have deteriorated. I have heard that this issue has been since rectified but only time will tell. I'm a bit square when it comes to my music and I prefer the analogue sound of LP's and tape. In the 80's I tended to buy tape recordings mostly classical for the simple reason that for the same money you could buy two or three classical recordings on tape for the price of one CD! I have recordings on tape that are approaching fifty years old and play perfectly. I do have some that suffer from drop out but they are a rare exception. The last time I catalogued my tape collection I had over 3000 of them, and yes I do have a listening programme, the nerd that I am, but I do have fun rooting about in second hand and thrift shops looking for tapes and LP's ,as this is the only place you can get them nowadays.    RE.Craig, Mon, 11th Feb 2013

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