Abstract: A method and apparatus for merging command/data packets from a plurality of parallel processing units into a concentrated data stream, while also providing for pipeline attribute data storage, direct user access to the pipeline, redirection of the pipeline, data insertion into the pipeline and pipeline diagnostics. The data from a plurality of parallel processing units is recombined in the same order as originally transmitted and then inputted into a buffer for entry into the pipeline. Attribute switching commands are deciphered by the concentrator of the invention and selectively stored and retrieved from the pipeline. New attribute values are passed downstream on command when they are different from existing attributes, or conversely, the concentrator may be overridden by the user so that attribute values supplied by the user may be stored and passed downstream. This technique thus minimizes repetitiveness in attribute switching.