When CDs are burned where does any aluminum oxide waste go? When 1s and zeros are burned into hard drives...?

Question

is anything being carved off by the laser, how can 1s and zeros or on and off codes be repeatedly 'burned' into the same tracks over and over? Is digital information just a speeded up version of Morris Code?

Answer 1

CD have a very thin layer of aluminum in which the data is embossed.

CD-Rs use a dye layer, usually cyanine. When it is "burned" it isn't actually oxidized because it is encased in the polycarbonate plastic of the CD and the air can't get to it. The laser just punches a hole by breaking down the dye and the material stays in the disk, just not so reflective any more. Once a CD-R is burned it stays burned.

CD-RWs have a chemical layer that can be erased and rewritten a number of times.

On a hard drive the codes are stored magnetically and this can be erased and overwritten any number of times.

Who said aluminum oxide is magnetic? That is nonsense. Disk drives nowadays use a cobalt alloy to record data.

Answer 2

Answering just your last question, since the other parts have been handled, Morse Code used a mix of long and short intervals to represent the alphabet. The alphabet can be represented with 5 bits (32 combinations) although more are needed for punctuation and keeping numbers and capitals separate. Braille uses 6 bits (dots) and ASCII uses 7 (for 128 possibilities).
The problem with digital is that digital codes can start with zero and Morse code, which people used to listen for, has to start with something. Also, listening to 7 or 8 identical bits is difficult. Electrically, digital requires some kind of marker to say "the character starts next" (start bit). These extra bits are what makes bits per second more like 10 or 11 per character instead of just 7.
Also, human effort was involved in Morse, so the most common letters were made short while less used ones were made of more combinations. Thus E and T have one dot and dash respectively, while A, I, M, N have 2, while X has 4 and all the numbers and punctuation have 5. All of these have 7 bits in ASCII. The spaces between characters have significance as word and sentence separators, so in effect Morse is a three level code, while in ASCII, period characters and carriage return characters are used.

Answer 3

Here is an interesting site discussing CDs.

http://www.chipchapin.com/CDMedia/index.php3

The data is encoded using an interleaved Reed Solomon algorithm, which adds redundant information. Because some of the information is redundant, it can be used to correct read (or write) many errors. This is why CDs are so scratch tolerant. The CD reader may not actually read the correct data on the disk, but the decoder detects and corrects these errors resulting in perfect playback. If there are too many errors for the decoder to correct, then it will cut-out and the CD becomes almost unusable at this point.

Here is a link on Reed-Solomon codes if you are interested.

http://en.wikipedia.org/wiki/Reed-Solomon_error_correction

Answer 4

CD's have little holes burnt into them and can't be re-written once they've been written once. But CD-RW the ones you can re write over again and again. They don't burn holes in the disk they do something else I can't remember. I think they may magnetize bits instead of making a hole. But anyway instead of reading 'holes' it just reads something on the surface. Thats why you need a special cd drive to read them.

EDIT: Okay I was wrong this is how a CD-RW works:

"While a prerecorded compact disc has its information permanently stamped into its polycarbonate plastic substrate, a CD-RW disc contains a phase-change alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium. An infra-red laser beam is employed to selectively heat and melt the crystallized recording layer into an amorphous state or to anneal it at a lower temperature back to its crystalline state. The different reflectance of the resulting areas make them appear like the pits and lands of a prerecorded CD."

Answer 5

aluminum oxide is a magnetic coating, on tape.hard drives hace a rigid magnetic disk.
cd's are hard plactic disks, and are pitted by the laser