1. An electro-optical computer having a memory comprising: (a) a machine-readable label holding a data file structure made up of a plurality of marks having one of two different states, said data file structure including (i) a plurality of codewords selected from a set of patterns of said marks, wherein each of said codewords represents at least one information-bearing character, and (ii) at least two rows of said codewords, wherein the codewords in one of said rows are members of a first subset of said set of mark patterns, and the codewords in a second one of the rows are members of a second subset of said set of mark patterns, the first subset of said set of mark patterns being distinguishable from the second subset of said set of mark patterns; (b) a system for reading the label and generating a signal representative of the codewords in said rows, said system being capable of concurrently reading a portion of the codewords from each of the two rows by distinguishing the first and second subsets; and (c) processing means, responsive to said signal, for processing the information-bearing characters in the codewords in said memory.