Abstract: A device and method for storing magnetically readable data are provided, the device including a disk having a substantially rigid, non-magnetizable substrate having a substantially planar surface and a magnetizable film having a substantially uniform thickness formed over the substantially planar surface. The disk has an outer surface having a nominal surface plane, and the outer surface includes a plurality of marks, each having a bump height above the nominal surface plane, a crater depth below the nominal surface plane, a mark radius, a bump radius of curvature, a crater radius of curvature and a separation from a consecutive mark, and at least one of the bump height, the crater depth, the mark radius, the bump radius of curvature, the crater radius of curvature and the separation is substantially randomly distributed according to any distribution of random variables such as, for example, a Gaussian normal, uniform, Poisson-like or Bernoulli-like binomial-like distribution.

Abstract: A magnetic tachometer for generating a signal as a function of the velocity of a transducer positioning arm in a disk drive. The tachometer is formed by a pair of fixed parallel coils separated by a distance sufficient to allow a magnet, attached to a counterbalance portion of the rotary positioning arm, to move therebetween and thus to generate a voltage as a function of the velocity of the magnet. The coils are each wound over a thin armature member which is saturated by the magnet's magnetic field and they are differentially coupled to produce common mode rejection.

Abstract: A method of manufacturing a magnetic tachometer used to generate a signal as a function of the velocity of a transducer positioning arm in a disk drive. The tachometer is formed over a one piece plastic insert having a first and second portion separated by a central breakaway region. An armature member is disposed over each of said first and second insert portion and a flexible connector is placed on a groove cut on a surface of said plastic insert. Two coils are simultaneously wound over said first and second insert portion, respectively, and connected to the flex connection. The insert is then bent to snap the breakaway region, and the resulting two coil subassemblies are folded and fastened to spacers to form a pair of fixed parallel coils. The separation between the coil is maintained at a predetermined value by the spacers to allow a magnet, attached to a counterbalance portion of a rotary positioning arm, to move therebetween and thus to generate a voltage as a function of the velocity of the magnet.