What materials are used to make a compact disk and how is music stored on one?

Answer 1

First, you need a background on binary.

Binary is a system of ones and zeroes (100101010101001001011 (I have no clue what that means, nor do I much care...)) used by computers and other electronics to store and send data. It is analogous to Morse Code - only think of it as Morse code with only on and off switches.

Now, binary digits all stand for numbers. Using one digit, we have 2 possible results:

0,1.

Which stand for the values of 0 and 1, respectively. Therefore, we call the first digit the "one's column"

If you know anything about basic permutations and statistics, you know this:

The number of permutations of anything equal the number of possibilities for an item, times the number of possibilities for the next item, and so on and so forth.

Therefore, we see that we have two possibilities for each digit; a zero and a one. If we have two digits, we have four possible choices - 2 (choices for the first digit) X 2 (choices for the second digit). Notice that this can be simplified by 2 squared (the use of the ^ sign will be used to denote exponents from here on, for means of simplicity), or 2^2.

As you may expect, with four digits, the number of possible combinations are 2^4, and, most importantly, with eight it is 2^8.

This is the number 256 (you would actually be able to count up to 255, since you still have 0 with 00000000). This amount of data is called one byte, and is the size of one letter, such as the letters on this page. This FAQ article is about the size of one kilobyte, or 1024 bytes (notice something? 1024 is a power of 2! It's like this in almost everything in computers and programming - check it out for yourself!!!). If I don't finish soon, it could be a megabyte, or 1024 X 1024 bytes, or a gigabyte, or 1024 X 1024 X 1024 bytes. That's a lot of information! This is how the computer stores, uses, and interprets all the information it has.

Now, with 255 characters, called ASCII (it's the computer's "alphabet"), the computer or CD player or whatever is able to translate these 0's and 1's into a sound wave based on what characters are present. Of course, this is an alarmingly high number of characters, but the computer is fast, and can probably handle it. If you were to try to decipher one song based on the information the computer sees, it could take you days, even weeks, to make it out, whereas the computer does it as it goes, at a standard rate called the "bit rate". One bit (Binary digIT) is one zero or one in a byte. As you may guess, songs with higher bitrates have better quality, but require faster processors and faster computers/CD players/etc. to play, and require more space on the disk.

Now, to answer your question, CDs are made of plastic. They hold information in binary like this:

___|__|___|__|_|___|____|__|_|_|_|_|.

If you think of zeroes as "off"s and ones as "on"s, it is easy to understand how they do this. The computer burning (making) the CD reads the binary information it wants to put on the CD, in your case, music, and literally burns a part of the CD with a laser to make it transparent (I don't remember if they burn holes for zeroes or ones, but one is burnt and the other is not). The distance between each bit is standardized, so the computer does not need to guess the size. As you can probably guess, these holes are very, very small. You probably normally couldn't see them, but they're there.

When your computer or CD player or whatever goes to read the CD, it uses another laser. When it detects the laser on the other side, it marks it down, and, by figuring out when it saw the laser, it is able to determine bits and bytes. If it doesn't see the laser, it will mark it as one thing, and, if it does, it will mark it as another. It then translates the bits and bytes (eight bits) into music, sound, movies, pictures, text, programs, or whatever you want to hear, use, see, do, or whatever.

This is actually the way most information is stored on your computer. It is also the way your hard drive works, but, instead of burning an optical hole, it uses tiny magnetic charges and a magnetic reader to keep track of data. That's why powerful electric storms can wipe out data on a hard drive of a computer.

DVDs work in the same basic principle, as well.

Does that answer your question?

Replyyes thank you! i actually kind of understand it :) is it just a piece of plastic with small holes that the disk is composed of then?

You can also find details on how compact discs are made from this article: http://www.newcyberian.com/CD-manufacturing.HTML