Magnetic hard drive

Even though the effect is small, magnetoresistance is used for sensing magnetic fields and for read heads on magnetic hard drives. 

In a computer hard drive, the data are stored on one or more rigid disks coated with magnetic materials. The magnetic film is coated on a planar NiP substrate. NiP film is typically electroplated on an aluminum disk. Before the coating process, the NiP must be planarized. The planarization process is similar to oxide ILD CMP except that the material is a metal. The slurry chemistry is similar to copper or tungsten CMP except that the end point is to form a perfectly planar substrate. Hydrogen peroxide can be used as an oxidizer in NiP CMP as stated in the patent by Jia and coworkers [14,15]. As shown in Fig. 7.5, the removal rate for NiP film follows the same trend as for copper. At higher concentration, the removal rate decreases because of the formation of a native protective NiO film [12]. 

Maintain a system for tracking the locations where electronic records are stored (hard drives on mainframes and personal computers, magnetic tapes, disks, CDs and other media). This system is required to enable timely retrieval of electronic data. 

In general, it is most efficient for the microprocessor to access and store in the semiconductor main memory (DRAM) alone because the DRAM access time is < 100 ns. However, DRAM is volatile and any information in the DRAM is lost once the computer is turned off. Thus, lower level of information storage devices is essential. The latter may include magnetic hard disc, magnetic floppy drives, etc. As a rule, the higher-level storage media are... 

FIGURE 33.20 Schematic of MFM of a magnetized pattern on a hard drive. 

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