Abstract: The present invention provides a method, system, and computer program product for extending channel programs in a computer system which uses a channel sub-system. An initial channel program is built to end with a terminating channel command word (CCW) followed by a dummy CCW. When required, a new channel program is built separately, then the dummy CCW in the initial channel program is modified to transfer channel execution to the new channel program. Once modification of the dummy CCW is completed, the terminating CCW in the initial channel program is modified to allow the newly-built transfer CCW to execute.

Abstract: A multi-path channel interface for computer input-output systems includes the ability to define and activate unbalanced groups of unidirectional communications sub-channels for a user application. Protocol independent exchange identifications permit not only unbalanced transmission groups but also allow user-controlled extensions for negotiating the values of transmission parameters at the time the transmission group is activated. When error correcting re-transmissions force the re-segmenting of data blocks, second level sub-segment indexing assure the proper order of delivery of the various segments and sub-segments. The exchange identifications include an identification of the user protocol being supported and thus permit interfacing with any user protocol.