Abstract: A dual magnetic head having a first magnetic core for reading and writing very high track density floppy disks and a second magnetic core for reading and writing conventional track density floppy disks. Neither the first nor the second magnetic cores require the trim erase elements associated with prior art magnetic cores for use with floppy disks. When writing on conventional track density floppy disks, separation between data tracks is achieved by erasing a circular region on a first rotation of the floppy disk, erasing a second region, separated from the first region by a small gap, on a second rotation of the floppy disk, and writing data during a third rotation of the floppy disk centered about the small gap. With very high density floppy disks, data is written directly between optical servo tracks on the floppy disk without use of the two erase steps.

Abstract: A diskette comprising a jacket, a liner material disposed within said jacket, a flat circular media having a magnetic coating on both sides disposed within said liner material, a hub attached at the center of said media, a plurality of servo grooves on at least one of said sides of said media that have stitched patterns that will alternate on-and-off at twenty kilohertz in the presence of a constant, unmodulated light source. The diskette is magnetically formatted with reference and data tracks recorded in such a way that extremely accurate position determinations can be made by looking at the analog amplitude of the detected tracks and comparing them at different head positions.

Abstract: A diskette comprising a jacket, a liner material disposed within said jacket, a flat circular media having a magnetic coating on both sides disposed within said liner material, a hub attached at the center of said media, a plurality of servo grooves on at least one of said sides of said media that have stitched patterns that will alternate on-and-off at twenty kilohertz in the presence of a constant, unmodulated light source. The diskette is magnetically formatted with reference and data tracks recorded in such a way that extremely accurate position determinations can be made by looking at the analog amplitude of the detected tracks and comparing them at different head positions.

Abstract: A method for inscribing data onto a magnetic medium (12) wherein portions of an oxide coating (16) of the medium are removed from the medium (12) to create voids (88) while the oxide coating (16) is left undisturbed on areas adjacent to the voids (88). The adjacent areas are then uniformly magnetized. When the medium is moved past a read head (78), changes in magnetic field present at transition points (82) and (84) between the voids (88) and the uniformly magnetized oxide coating (16) of adjacent areas cause a current to be induced in a coil (80) of the read (78) head which current is interpreted by conventional read circuitry as being a data bit. The data inscribed by this method is not erasable by conventional means. The inventive method may be practiced upon selected portions of a medium (12) such that non-erasable data areas and conventional magnetically erasable data areas can coexist on the same medium (12).

Abstract: A magnetic information storage medium, such as a floppy or rigid magnetic disk, and an apparatus and method for inscribing a plurality of indelible grooves in a surface of the medium to function as optical servo tracks. The grooves can be in the form of a plurality of continuous or noncontinuous concentric circles. The grooves can also be a continuous spiral or a plurality of continuous concentric circles having non-constant widths and/or depths. The apparatus comprises a platen and drive motor for rotating the medium, an argon ion laser light source for generating a beam of light, optical components for directing the beam of light to a beam focusing carriage and a microcomputer for controlling the apparatus. The method involves rotating the medium under the focused light beam to inscribe the grooves on the surface of the medium. Optical track densities greater than 1000 tracks per inch can be obtained with the method.

Abstract: A flexible magnetic medium having a plurality of optical servo tracks indelibly marked on the medium and a method for stamping the tracks on the medium. The optical servo tracks comprise a plurality of circular concentric regions positioned on a face of a floppy disk with each circular region comprising a plurality of pits. The optical servo tracks are imprinted on the floppy disk by placing a stamper disk bearing a template of the optical servo tracks in a hydraulic press and pressing the stamper disk and floppy disk together, typically under five to nine tons per square inch of pressure.

Abstract: An optical servo head and method for reading position information on a medium, such as a magnetic disk, having a plurality of optical servo tracks in the form of relatively nonreflective regions on a reflective surface of the medium. With a magnetic disk, the nonreflective regions comprise concentric grooves etched in the disk surface and the reflective regions comprise the land areas between the grooves. The optical servo head is mounted on a carriage/head assembly of a disk drive and comprises an infrared light emitting diode, a collection lens, a routing mirror and a multicell photodetector.

Abstract: A magnetic information storage medium, such as a floppy or rigid magnetic disk having a plurality of indelible grooves inscribed on a surface of the medium to function as optical servo tracks. The grooves can be in the form of a plurality of continuous or noncontinuous concentric circles. The grooves can also be a continuous spiral or a plurality of continuous concentric circles having non-constant widths and/or depths.

Abstract: An optical servo head and method for reading position information on a medium, such as a magnetic disk, having a plurality of optical servo tracks in the form of relatively nonreflective regions on a reflective surface of the medium. With a magnetic disk, the nonreflective regions comprise concentric grooves etched in the disk surface and the reflective regions comprise the land areas between the grooves. The optical servo head is mounted on a carriage/head assembly of a disk drive and comprises an infrared light emitting diode, a collection lens, a routing mirror and a multicell photodetector.

Abstract: A magnetic medium including a physical reference feature for conveying positional information to a magnetic read/write head. The reference feature is made by indelibly marking a pattern on a surface of the medium such as by inscribing the metal oxide coating on the medium surface or by chemical etching or photolithography of the surface. Magnetic data is written on the surface of the medium and when data written on the reference feature is read, a modulated read back signal is observed which indicates the position of the reference feature. The position of the reference feature is used to direct the read/write head to track zero or to some other position on the medium surface. By using a second magnetic read/write head to write data on a second surface of the medium in response to the modulated readback signal, an electronic reference track can be written on the second surface for providing positional information to the second magnetic read/write head.

Abstract: Correction of the ellipticity of a diode laser beam is achieved by an anamorphic beam expansion prism pair that are separated by an angularly rotationally adjustable mirror. The first prism of the prism pair is rotationally adjustable to various detent positions about a first axis and is translatable to various detent positions along a second axis, while the second prism has a fixed position. The first prism provides some beam expansion and the second prism provides the remainder of the beam expansion. The amount of beam expansion by the first prism is varied by adjustment of its rotation and translation, yet the expanded beam from the first prism exhibits zero positional offset at the location of the rotatable mirror. The mirror is rotated such that the optical axis between the mirror and the second prism is the same for all cases of beam expansion.

Abstract: A system for providing a read signal from a magneto-optic medium wherein a non-rotated leaky beam splitter is utilized to provide both s and p components of the light reflected from the medium to a differential detector arrangement. The beam splitter, which may be of conventional construction and which has the reflected beam striking its medium-facing face at normal incidence, is operated in a leaky mode by utilizing it with a read beam having a wavelength differing from the wavelength for which the beam splitter was designed. One face of the beam splitter can be cut at a small angle off normal to prevent any p-polarized light from entering the differential detector arrangement directly from the light source.