Coding for New Applications in Storage Media Doctoral Thesis Research Proposal

Conventional magnetic recording media are composed of basic magnetizable units called grains which might be random in size and shape. Information is stored on the medium through a write mechanism that sets the magnetic polarities of the grains. Each grain can be magnetized to take on one of the two possible types of magnetic polarity. Thus, each grain represents at most one bit of information. If the boundaries of the grains had been known to the write and the readback apparatuses, then, theoretically, it would have been possible to attain the storage capacity of one bit per grain. However, even if the write and the readback apparatuses were aware of the shapes and locations of specific grains in the medium, it would still be impossible to attain the capacity of one bit per grain since the existing technologies are still incapable of setting magnetic polarities of regions as small as a single grain. In current technologies, the writing in a magnetic medium is carried out by dividing the medium into periodically partitioned cells and writing one bit of data into these cells. Since a cell is typically larger in size than a grain, the writing of a bit into a cell boils down to uniformly magnetizing all the grains inside the cell (whereas the grains straddling the boundary between cells can be neglected). Sometimes it is useful to view the recording medium as a channel that is a “black box” with inputs and outputs where output can differ from the