1. A data processing system, having a plurality of processing units, comprising: a cache for storing data to be utilized by said processing units; a system bus for transferring data between said cache and said processing units; and circuit means for transferring, in a single operation, input data to said cache from said processing units and output data from said cache to said processing units, in an amount greater than a capacity of said system bus, said circuit means sequentially storing said input data as data words, combining adjacent ones of said data words and providing said combined data word to said cache; wherein said single operation simultaneously transfers said data between said cache and said plurality of processing units.