Principle of Magnetic Recording in Computer Data Storage

PRINCIPLE OF MAGNETIC RECORDING IN COMPUTER DATA STORAGE

Now a days, large number of informations are stored in (or) retrieved from the storage devices, by using the magnetic phenomena. The main part of these magnetic storage devices is magnetic recording heads and they function according to the principles of magnetic induction.

Generally ferro or ferrimagnetic materials are used in the storage devices, because in this type of materials only the magnetic interaction between any two dipoles align themselves parallel to each other. Due to this parallel alignment, even if we apply small amount of magnetic field, a large value of magnetisation is produced. By using this property informations are stored in the storage devices.

In the storage devices, the recording of digital data (0's and 1's) depends upon the direction of magnetisation in the medium.

Magnetic parameters for recording

1. When current is passed through a coil, a magnetic field is induced. This principle, called "electromagnetic induction" is used as a basic parameter in the storage device.

2. The ease with which the material can be magnetised is another parameter.

3. We know the soft magnetic materials are the materials which can easily be magnetised and demagnetised. Hence based on this parameter, a data Le can be stored and erased easily. Such magnetic materials are used in temporary storage devices.

4. Similarly we know hard magnetic materials cannot be easily magnetised and demagnetised easily. So, such magnetic materials are used in permanent storage devices.

5. In soft magnetic materials, the electrical resistance varies with respect to the magnetisation and this effect is called magneto‒resistance. This parameter is used in specific thin film systems.

Note: If the change in electrical resistance is very high compared to the magnetisation, it is called GIANT MAGNETO‒ RESISTANCE (GMR) effect.

Magnetic Medium

Magnetic medium is made of magnetic material (ferrous or ferric oxide) deposited on in plastic as shown in Fig. 1.25.

Read‒Write Mechanism

The magnetic medium move across the read/write heads and either logic 1's or logic 0's are written on the medium. Then, the medium moves across the head again, the magnetised spots on the medium generate small electrical signals and this different direction signals represent logic 1's and 0's on the medium.

Now, when the recorded medium moves over the read head, the change in magnetic field generates very small signals in the head winding and they are amplified. From this the logic signals 1's and 0's are read depending on the data stored on the medium.