Abstract: Digital circuitry performs arithmetic operations upon first and second binary coded decimal digit strings input thereto. The digital circuitry provides for receiving and storing a first and second BCD digit, the digits having an arbitrary data type format. The first and second data types are selected from the group of packed and unpacked data. The circuitry then performs the arithmetic operation upon the stored BCD digits to obtain a result data word which is made available in a data type format corresponding to a selected one of the input BCD digits. In a particular embodiment, a plurality of the circuits can be operated in a digit slice structure. The digit slice structure operates upon strings of packed, unpacked, and mixed data type arithmetic operands and provides, at its output lines, output data in a format corresponding to a selected input data type. In particular, a unique interconnection of the plural output lines of the circuitry enables the output data type to be packed or unpacked as desired.

Abstract: Apparatus is disclosed for reading phase encoded digital data from a nine-track magnetic tape which apparatus includes timing circuitry for deriving a clock signal from the recorded data. A portion of the timing circuitry is associated with each track on the tape and automatically accommodates, without generating errors, phase changes in the derived clock signal in that track caused by speed variations in the magnetic tape transport and due to bit shifts caused by certain data patterns.Tape transport speed variations are sensed and the derived clock rate is corrected by a digital phase-locked loop which uses a counter that is clocked at a constant rate to determine the timing "window" during which the circuitry looks for signal transitions on the magnetic tape. A running average of the count remaining in the counter at the time when a transition actually occurs is used to adjust the counter starting value until equilibrium is established.