Abstract: A fiber optic detection system in which a single optic fiber has a U-shaped configuration. A source of light is disposed at one upper free end of the optic fiber and a light detector is disposed at the other upper free end of the optic fiber. At the bottom of the optic fiber is a light variable loop adapted to be disposed in various media, such as liquids, fluids and air. The light from the source of light is conducted from the source of light through the optic fiber and to the light detector. The quantum of light lost as the light travels through the light variable loop will depend on the medium or the concentration of the medium in which the light variable loop is disposed. The light detector detects the light advancing thereto to produce a signal representative of the medium or the concentration of the medium in which the light variable loop is disposed.

Abstract: A disk drive system includes a disk controller system having separate head positioning and data transfer subsystems and supporting up to four disk drives, two of which may be removable and two of which may connect through a standard ST506 interface. The system provides a read and write protected cylinder for removable drives, a read only cylinder for removable drives which may store a unique serial number as well as other write protected data, and a high capacity, high speed sector buffer which allows continuous transfers of data to or from noninterleaved sectors and supports concurrent disk and system accesses.

Abstract: A method of run-length-limited encoding strings of data including a sequence of synchronizing bits having a value of binary zero for providing corresponding encoded bits which, when recorded on a magnetic storage medium, provide a maximum number of flux transitions. The steps of this method include serially receiving such a string of input bits, dividing the string of input bits into unique bit groups, replacing each group with a corresponding collection of encoded bits conforming with the limitations of the run-length-limited encoding scheme, including replacing each divided group of three input binary zeros into a collection of six encoded bits having two binary ones separated by two binary zeros, serially transmitting these collections of encoded bits for recording the same on the medium in the same sequence as the corresponding input bit groups are received.

Abstract: A combined serial priority and parallel priority apparatus and method of operation for use in data processing systems. Each of the parallel priority circuits are interconnected by a common parallel priority bus which carries parallel priority signals indicating the priority level of any unit requesting access. If a unit requesting access has a lower priority than indicated on the parallel priority bus, that requesting unit is inhibited from obtaining access. If a requesting unit has higher priority than the signals on the parallel priority bus, that unit in turn causes the priortiy bus to be switched to the higher priority level.The serial priority circuits act together with other serial priority circuits within a group of priority circuits set to the same parallel priority. In this configuration, the parallel priority circuits perform a high-order priority determination while the serial priority circuits perform a low-order priority determination.