Internet of access mechanism

Data are recorded on the tracks of a spinning disk surface and read from the surface by one or more read write heads. As shown in figure 6.4 the read write heads are mounted on an access arms assembly. Most disk drives have a single read write head for each disk surface. However some faster disk systems use multiple heads on each access arm to read a number of adjacent tracks simultaneously.

     The access arms assembly can be moved in and out In the direction shown in the figure 6.4 so that the read write head can be moved horizontally across the surface of the disk. In this manner the read write heads can be positioned on any track on which data are to be recorded or from which data are to be read.

The read write heads are of flying type. That is they do not have direct contact with the disk surface. This prevents wear on the surface of the disk. A separation of about 0.00002 inch is maintained between a read write head and its corresponding disk surface. In fact read write heads fly so close to the disk surface that , if a dust particle(typically of 0.0015 inch size), smoke particle (typically of 0.00025 inch size), finger print (typically of 0.00062 inch size) or a human hair (typically of 0.003 inch size) were placed on the disk surface, it would bridge the gap between the write heads and disk surface, causing the head to crash. A head crash, in which the head touches the disk, destroys the data stored in the crash and can destroy a read write head as well.