Abstract: The Channel Bus Controller (CBC) transfers information between groups of input/output channels and processor storage. Storage receives or dispenses two data words per access operation. Interfaces for transfers from the channel groups to the CBC are advantageously one word wide; since each output (fetch) request consists of a single request word. Information sent by each group is assembled into three-word units (a request word and zero, one or two data words) in a respective channel bus assembly register (CBAR). The assembled unit is passed from the CBAR to a respective area of an In Buffer array and from that array to storage. Zero filler words are inserted into unused data word positions. A channel request may be tagged to designate a transfer of four data words. If the transfer is an input the four data words are sent to the CBC with a single request word.