Abstract: A data storage disk having a latent illuminance discrimination marker for determining whether the data storage disk is suitable for use in a disk drive. A light source illuminates the marker and the marker emits illuminance, preferably as phosphorescence. A detector detects the emitted illuminance, and a predetermined characteristic of the marker in the frequency domain is determined. The frequency domain response may be either a phase response or an amplitude response, or both. The frequency domain response provides identification of different types or generations of data storage disks or provides a secure keying mechanism for authorized access to proprietary software.

Abstract: A link detection circuit automatically terminates SCSI data transmission lines by use of a sense circuit which detects the absence or presence of an adjoining device or devices. The lines are automatically terminated at the ends with no user intervention. Wrong input/output cabling is precluded by use of a bi-directional link detection circuit. Detection is done without adding signal lines or disturbing buss functionality.