The magnetic card is made by uniformly coating a layer of magnetic particulate material on a piece of plastic. The magnetic particles on the newly produced magnetic card are not magnetic. Such a magnetic card is like a piece of white paper. People need to input some information into the magnetic card to use. So how is the information recorded? This requires the help of the recording head.
A recording head is a device that, when current is applied, produces a magnetic field proportional to the current. People control the device to pass the magnetic card through the recording head, and the magnetic particles on the magnetic card are magnetized.
If the signal current is varied, this current can express some kind of information, and the magnetic body on the magnetic card is magnetized to varying degrees with the change of the current. After the magnetic card is magnetized, the card is left with the same magnetic current as the current change. At this time, the magnetic card also records the information sent by the current, thus having its identity.
According to the rules set in advance, people can know what information is included on the magnetic card when needed.