So I was watching this (https://www.youtube.com/watch?v=WkIR23emsWY) by technology connections and I just realized that I have no idea how CDs work. The video is about how some CD players can read audio of a CD where the data is just copied directly onto a CD with a computer whereas older players only had hardware compatible with CDs formatted as …. digital audio?
I was trying to figure it out on wikipedia, how is a commercial CD you’d buy in a store different from a CD with files copies onto it?
I remember my dad used to use a burning tool to make images. Why are they called images? How is an image different from a CD?
Why are some CDs readable and writable but some aren’t?
In: Technology
A commercial CD that you’d buy in a store, like a music album, is usually what’s called a “pressed” CD. During manufacturing, data is physically stamped into the disc in the form of microscopic “pits” and “lands”. These represent the digital information (as zeros and ones) that is read by a laser in your CD player. These discs are read-only; you can’t change the data on them.
On the other hand, when you copy files onto a CD with a computer, that process involves “burning” the data onto the disc. This happens with a special laser that changes the surface of the CD-R (CD-Recordable). Unlike pressed CDs, these discs have a special dye layer that the laser alters to simulate the same pit-and-land pattern used in commercial discs. When your computer burns the data, it uses this dye to create marks that a CD player can read. CD-RWs (Rewritable) go a step further: they use a special dye that allows the laser to erase and rewrite the data multiple times, however after a few rewrites, these discs can wear out.
Now, these are the differences on the hardware level. However, there are different ways how the information can be stored on the software level. Pure digital audio (also called a “red book” CD) is basically the digital equivalent to an old analog record. It contains only the raw audio amplitude samples from the audio track similar to how an anlog record contains the track as a groove. Its a very simple format, and it can only store raw, uncompressed audio. Music CDs from a store typically are in this format and and old CD players can only play back this.
Contrary to the red book CDs it is also possible to create a full file system on a CD, similar to a USB thumb drive. This way it is possible to store arbitrary files on the CD, not only audio. And the audio that you do save can be in an abitrary format, even compressed like MP3. Reading those CDs is much more complex which is why old CD players cannot do it.
A CD image is just a big file on your computer containing a one-to-one copy of the bits on a CD. This way you can store and copy a CD without having to open or understand its contents.
Latest Answers