Fibre channel input/output data routing system and method

A method for performing an input/output (I/O) operation between a host computer (102) and control-unit (118) comprises obtaining information about the I/O operation from a channel subsystem (128) in the host system, the channel having a local processor and memory. An Address Control Word (ACW) (Fig 11) is generated and specifying the memory location and including a field for storing header information for use in one or more messages transmitted between the channel subsystem and the control unit. An address control structure (Fig 5) for each data transfer in the I/O operation is generated and forwarded to the network interface between the channel subsystem and I/O device and specifies a location in the local memory of the ACW. On receipt of an I/O command message via the network a data transfer request from the network interface is issued and includes addressing information. In response to a data store request including a header the data is routed to the memory location stored in the ACW and the header stored in the corresponding ACW. In response to a data read request including a header the data is retrieved from the host memory location specified in the ACW and header information is appended to the data.