Abstract: A method is provided for decoding an input data stream formed of data words aving word boundaries and a synchronization word in a network interface unit of a high speed computer network. The input data stream is applied to a serial-to-parallel shift register to provide parallel boundary determination words for locating a word boundary within the data stream. There no serial shifting of bits within the parallel boundary determination words. The parallel boundary determination words are shifted through a register file in parallel and applied to synchronization word detectors which provide a series of detecting windows shifted from each other by one bit. When one of the word detection windows detects the synchronization word a word boundary is determined in accordance with the detection. Boundary detection data is thus effectively monitored in serial while it is shifted through the register file in parallel. This permits the use of slower and smaller logic in the register file.