Hard disk drives once used combined inductive read/write heads. Today, high?performance drives have GMR read?heads.

Question

a. What is a GMR read?head?
b. What are the advantages of separate read and write heads?

Answer 1

a. First?generation read/write heads used a coil of wire on a ring with a tiny gap in it. During writing, a
current in the coil generated a field in the ring that leaked out of the air?gap in the ring and into the
surface of the disk. When reading, the magnetic field from the surface leaked into the ring and induced a current in the coil.

The GMR head uses the giant magnetoresistive (GMR) effect that was discovered in the 1980s. It was
found that certain thin layers of magnetic elements displayed a remarkably large change in electrical
resistance under the influence of a magnetic field. Scientists at IBM applied the discovery to the creation of practical GMR read heads to detect the magnetic flux from the surface of a disk. That is, conventional read heads detected the recorded flux by detecting an induced current in a coil, whereas GMR heads detect a change in electrical resistance due to the magnetic field.

b. The advantages of separate read and write heads is that each head can be optimized for its task. If a coil is used, there is a conflict between reading and writing (the read coil needs a lot of turns to detect the signal, and a write coil needs few turns to reduce impedance and allow faster writing). By using a GMR head for reading (which has low inductance), high speed is possible and the write head can be optimized entirely for writing.