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 having an error checking field is stored in the local memory. 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. A data route in the channel compares the ACW error checking field and the address control structure error checking field and if they match, the corresponding ACW is retrieved and used to route the data transfer request to the host memory (106) specified in the ACW.