History and DevelopmentThe primary computer storage medium, before the introduction of magnetic storage, was punch cards. These were paper cards with holes punched in them to indicate binary data invented by Herman Hollerith in the late 19th century. In June 1949, a group of IBM scientists and engineers began work on creating a new storage device that would soon revolutionize the industry. May 21, 1952 marked the transition from punched card calculators to electronic computers when IBM introduced the IBM 726 tape drive [1]. It was used to store data in IBM's first commercial scientific computer intended to help the US military design aircraft.[2] Four years later, IBM manufactured the first computer disk storage system: the RAMAC 305 drive. Although this drive could only store 5 MB of data, the information could be stored directly anywhere on the disk surface without having to read all the intermediate information, as was the case on magnetic tapes. This ability to access random locations had a very large effect on computer performance and allowed data to be stored and retrieved much faster than tapes. The next 60 years saw enormous advancements in the magnetic storage industry, from a variety of hard drives to portable memory such as cassettes, floppy disks and zip drives. Today, we can store even 3TB of data on tiny 3.5-inch drives. This was all possible thanks to electromagnetism and the magnetic properties of ferromagnetic materials such as iron oxides[add the magnetism part]In 1819, a Danish physicist Hans Christian Oersted was preparing his materials for an experiment when he did a brilliant observation. He noticed that when the needle of a compass was brought close to a wire carrying an electric current, the n...... middle of paper......f the head. As a result, the magnetic field due to the head polarizes the magnetic particles it passes directly through the medium and aligns them with its field. Depending on the flow of electric current through the coils, the polarity of the head field and the induced field in the magnetic medium changes polarity. Therefore, when the magnetic field passes through the medium, the particles that lie just below the air gap tend to align in the same direction as this field. Once the individual magnetic dipoles of the particles are aligned, they no longer cancel and a net magnetic field is observed in this region. Many magnetic particles now work together to produce a cumulative field in the same direction. Due to the hysteresis properties of ferromagnetic materials, individual particles retain their magnetic dipoles as well as the net field.