The rate of development in modern digital computer systems and software has led to an almost insatiable demand for ever increasing storage capacities. In response to this demand the memory manufactures and, in particular the disk drive manufacturers have over the last decade or so come forward with spectacular increases in storage capacities and densities. The ?eld of magneticmemoryhasbeenonthefrontierofadvancedmaterialsdevelopment for many years. The momentum now gained in the technology is such that storage densities are increasing at something like one hundred percent per annum and this rate may still be rising. Over the past decades dramatic progress has been made in magnetic storage systems. In the past few years 2 areal densities, currently above 50 Gbits/in , have doubled every 10 months 2 and are expected to reach 100 Gbits/in in the near future. The price per megabytehasdecreasedbyafactorof10inthelastdecadeandispredictedto drop to USD 0. 05 ber megabyte within the next 10 years. The reason is that the intensive investigations in the ?eld of the nanoscale magnetic materials promote to the great progress in various kinds of the magnetic storage media (computer ?oppy disks, sound/video tapes, etc. ). Among the magnetic storage devices, the hard disk drive (HDD) is the dominant secondary mass storage device for computers, and very likely also for homeelectronicproducts in thenear future. The HDDis an integration of many key technologies, including head, medium, head-disk interface, servo, channelcoding/decoding,andelectromechanicalandelectromagneticdevices.