CDR Capacity: What's the Difference Between a 74min and 80min CD?

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In summary, the difference between a 74min and 80min CD is the amount of error checking and correction data written on the CD. This allows a data CD to hold more data, while an audio CD can hold more minutes of audio. This is achieved through a finer pitched timing track on the CD, with improved surface coatings allowing for more data to be written. There is no actual "gnome" involved in the process, just advanced technology and manufacturing techniques.
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What is the difference between a 74min and 80min CD?

I was just recording to my scratch CD and noticed that it had passed the 645Mb limit of a 74min CD, therefore it must be 80min.
I base a CD's capacity on how wide the unwritten stripe is, but I wondered how the CD Writer knows the difference?

I assume the CDs are the same physical size, and the laser diode tracks and pulses at the same rate and the disk spins at the same speed. So there must be something else clever, like a small gnome that twiddles a small screw in the CD writer.

Any clever people out there who can confirm my gnome theory, preferably with photographs; or alternatively any crack pots with ridiculous off the wall theories about how it could be done with technology?
 
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Writeable CDs are manufactured with a spiral timing track already written on them. The CD writer follows that track to control the rotation speed and laser position.

The basic difference between audio and data CDs is that data CDs have more error checking and correction data written on them. Therefore you can get 80 minutes of audio on an audio CD, but only 74 minutes of audio in a .wav file at 44.1Kz stereo on a data CD.

Reading an audio CD, the player can interpolate some plausible-sounding data (pun intended) if it finds an uncorrectable error. That is not possible for a computer data file - the only option is to display an error message and stop.
 
  • #3
Ahhhh...
So a 700Mb (80min) CDR has a finer pitched timing track than a 650MB (74min) CDR.
Obviously the surface coatings improved by about 10% at sometime, I think even budget CDRs are 700Mb now.

So where does the Gnome come into it?
 

What is CDR capacity?

CDR capacity, or carbon dioxide removal capacity, refers to the ability of a system or technology to remove carbon dioxide from the atmosphere or other sources.

What are some examples of CDR technologies?

Examples of CDR technologies include carbon capture and storage, afforestation and reforestation, bioenergy with carbon capture and storage, and direct air capture.

What is the role of gnomes in CDR capacity?

Gnomes have no role in CDR capacity. This term is likely a misunderstanding or a joke, as gnomes are fictional creatures and have no involvement in scientific concepts such as CDR.

How is the effectiveness of CDR technologies measured?

The effectiveness of CDR technologies is measured through various factors such as the amount of carbon dioxide removed, the cost of implementation, and potential environmental impacts.

Why is CDR capacity important?

CDR capacity is important as it can help mitigate the effects of climate change by reducing the amount of carbon dioxide in the atmosphere, which contributes to global warming. It can also help offset emissions from other sources and achieve carbon neutrality.

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