A transducer is the broad name for a device which transforms energy from one form to another. We will discuss magnetic heads later, but first we are going to look at the media, the tape or disc which stores the magnetic energy, and how it is designed and made to enable us to be able to store data. We need this form because we have to have something which is can be magnetized and have a size and shape which is readily magnetizable, and one whose state can readily be determined. We use these particles to induce a magnetic field into a transducer - which in this case is a magnetic head. To describe it crudely, magnetic tape is nothing more than rust on tape.
Magnetic tape consists of a base - the carrier for the 'rust'.
Today we see different forms of plastic material for the base. However the base could be any flexible material capable of being magnetized. Some of the early experiments were used long metal bands. In the US the first tape seen by the general public was a paper base with a magnetite coating. Over the years tape technology has evolved to a very high level - but at the heart it is really just a long band of flexible magnetizable material.