New heights for hard disk drives

Such tremendous storage density growth has permitted the HDD to be made much smaller.The very first generation of HDDs had dimensions on the scale of a storage cabinet, whereas the micro-drive developed by IBM in 2000 was small enough to fit in an eggshell and had a storage capacity over 1 GB.The technologies involved in building a HDD are truly interdisciplinary, including coding and signal processing, electromagnetics, materials science and engineering, magnetism, microfabrication, electronics, tribology, control systems, heat transfer, and so on.However, the scope of this article will be limited to the magnetic aspect of data storage and retrieval mechanisms in a HDD. Storing bitsIn a HDD, binary data are stored in a thin magnetic layer, called the recording medium, deposited on a substrate.A '1' bit is stored as a local magnetic moment reverses its orientation along the circumferentially arranged data trackthe magnetization transition, whereas a '0' bit corresponds to no change of the local moment orientation (Fig. 1).Since the magnetic moment orientation representing the stored bits is in the direction of the recording track, this mode is referred to as longitudinal recording (Fig. 2).Magnetic hysteresis of the recording media enables the retention of the local magnetic moment orientation and, thereby, data.The disk rotates at a constant speed, which ranges from 3600 rpm in a low-end product to 15 000 rpm in a high-end product.Meanwhile a recording head, consisting of both write and read elements embedded at the end of an air-bearing slider, flies over the disk surface at a steady clearance of 5 nm.The by Jian-Gang (Jimmy) Zhu New heights for hard disk drives