How is music recorded into a vinyl record and how is it "read"?

Al have given a great description of the creation of records, but for you younger folks there is still some confusion about how the data is "read". Let's back track a bit. "Sound" is in fact minute changes in pressure in the air. A microphone takes those changes in pressure and converts them to a changing electrical impulse. When a record is produced we take those changing impulses and turn them into changing depths in the record groove. The physical depth of the cut in the record groove corresponds to the air pressure changes in the original song. Now, how do we "read" that data? Simple, we must "read" the physical depth of the cut and use it to vary the air pressure in our listening environment. Now, we could do this using electronics, but the simplest way to do this is to use a thin stylus to pick up the depth of the groove and then use that stylus to vibrate a rigid membrane, thereby causing air pressure changes in the listening environment, which our ears will perceive as "sound". If you are over the age of 40 or so, you will have almost certainly done this as a kid, but for the rest of you here's a great demo: Now, for the added bonus answer: what about stereo? With stereo there are two channels, left and right. The earliest attempts to record two tracks were somewhat comical: The winning design had two very important features: 1) It was able to record and play back stereo sound with only a single needle 2) It was backwards-compatible with mono recordings, so that a mono player could play a stereo record and also a stereo player could play a mono record. How did they do this??? Have a look: http://www.vinylrecorder.com/stereo.html