The magnetic card is made by coating a layer of magnetic particle evenly on a piece of plastic. Just produced magnetic particles above the magnetic particles are non-magnetic, such a magnetic card is like a piece of white paper, people need to enter some information in the magnetic card to use. How is the information recorded? This requires the help of a recording head.
The recording head is a device that produces a magnetic field that is proportional to the current once it is energized. People control the device so that the magnetic card through the recording head, the magnetic particles on the magnetic card is magnetized.
If the signal current is changed, this kind of current can express some kind of information, and the magnetic substance on the magnetic card will be magnetized to some extent with the change of the current. After the magnetic card is magnetized, the card will have the same magnetic property as the current variation law. At this moment, the magnetic card records the information sent by the current, so as to have its identity.
People according to pre-set rules, when needed, you can know what information is included on the magnetic card.