Abstract: The functionality of “protected shareware” is controlled by digitally signed messaging protocol. Protective code within the shareware controls the functionality of the shareware in response to authorization messages which are supplied directly or indirectly by the shareware supplier. These messages are digitally signed in whole or part by or on behalf of the shareware supplier using the supplier's secret signing key. The shareware, in turn, includes the public checking key for this digital signature of the supplier, thereby enabling the protective code to authenticate any such authorization message before acting in reliance upon it. The shareware includes an integrity self-checking routine which is run at appropriate times to ensure that shareware, including its protective code, is in an anticipated state. Typically this is equivalent to a finding that the code has not been altered, but it is conceivable that the code might be dynamically altered in some authorized (i. e.

Abstract: The spindle for a disk drive comprises a dish-like hub for centering a removable disk-like recording media and a magnet chuck for clamping the recording media against an axial position reference surface on the hub. To stabily center the recording media on the spindle to provide a reference surface for controlling the axial positioning of the media, the hub has a central conical post which extends axially of the spindle beyond the plane of a radially displaced annular rim or flange. The post narrows toward its free outer end with a fixed taper, so that the recording media seats thereon and makes interference contact therewith before reaching the plane of the rim. To clamp the disk to the hub and to seat it against the rim, there is a magnetic chuck comprising an annular magnet which is disposed between the post and rim and a strike ring which is engaged with or embedded in an inner circumferential portion of the disk for deflecting the recording media into contract with the rim.

Abstract: An electro-optic device for use in optical modulating systems and the like comprises a pair of optically transparent, multi-element interdigital electrodes which are sandwiched between a pair of electro-optic crystals, whereby symmetrical fringing fields having a predetermined periodicity widthwise of the device are coupled into the crystals when a voltage is applied to the electrodes, thereby creating substantially identical phase diffraction gratings in the crystals for sequentially diffracting an incident optical beam.