We all know that DVDs work just like a record player except it reads holes or bumps and raised areas with a laser instead of a record needle. If we had a disc and laser reading variations of vibrations of electricity, we then would have unlimited or extremely large amounts of space to put information of movies or computer data on. If the disc was reading electrical signals along with bumps AND dips in grooves we would have two, or more, forms of readable info making it hold more info. It would read the bumps and grooves but, it would read an electrical wobble in it as well.
You know how a DVD can skip and you loose the picture? What if it read those skips as vibration information. It would literally tip and read that difference. So we would have a three-dimensional tip and with the electricity storage surface where the bumps and hills are in, the grooves are read as readable variations. Just a slight tip would mean something to the reader of the electrical output. Like a computer hard drive with bumps and grooves. Two or more forms of info. The electricity could be static, wobbles in the DVD, magnetic or, all three with the usual laser read hills and holes as well.