Proffesional CD's and DVD's aren't burned, but they are pressed. A master copy would probably be burnt and used to make a molding to press the CD's in the factory.

DVD's sometimes have dual layers, and with this each layer is pressed seperately and then joined together before being pressed onto the plastic disc.

CD and DVD burners that you can buy obviously can't press the discs, so what they do is heat up the disc in certain places to create a sort of dent in the disc, which the computer (or any cd player) reads as a pit.

VHS would not degrade too much if stored properly, but playing them time and time again does degrade the picture; hence I am really looking forward to the Star Wars DVD's in september as my VHS copies (of the pre 97 special edition) have degraded quite a lot, so the picture is very bad.

VCD uses MPEG-1 compression, but only uses a bit-rate of 1150 kbps with a picture size of 352 x 288 .... which means that it is only as good quality as an old VHS tape.
It is possible to use different types of MPEG encoding to produce higher qualities; such as SVCD which uses MPEG-2 and a higher bitrate and larger picture size.
There is also KVCD which uses an altered encoding format to produce higher than VCD quality footage but fitting up to 2 hours onto a single 80 minute CDR.
XVCD is highest quality, and it uses a bitrate of around 3.5mbps, so you'd get close to DVD quality, but only be able to store about 30 minutes on a single 80 minute CD.


DVD is of course the ultimate quality format, using encoding bitrates of up to about 12mbps, and AC3 audio encoding of up to 448kbps.