Magnetic Data Storage
The basic principle of magnetic data recording is the defined magnetising of smallest areas of thin hard magnetic layers deposited on suitable carrier materials (aluminum or special glass disk, plastic film).
In the picture an open hard disk drive is depicted with
- a magnetic disc
- a write-read head
The approximately 15 nm thick magnetic layers of the discs are composed of hard magnetic particles (average size < 10nm).
They are magnetised bi-directionally in the magnetic field of a write-read head.
The binary numbers of 0 and 1 are assigned to the two states with positive and negative remanence.
Because of the size of the write-head, in general each several hard magnetic particles with the same magnetisation are 1 bit.
For magnetisation and recording can be used either
- longitudinal (magnetic ) recording
- perpendicular (magnetic) recording
Both principles are compared below.
The direction of the magnetic field can be reversed in the write-head within a very short time.