Patent ID: 8055807

Claim:
A computer program product for processing a chain linked transport control channel program at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system, the computer program product comprising: a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: receiving a first command message at the control unit from the I/O subsystem, the first command message including a first set of one or more I/O commands to be performed and specifying a first predetermined sequence number for performing the first set of one or more commands as part of an I/O operation; receiving a second command message at the control unit from the I/O subsystem, the second command message including a second set of one or more I/O commands to be performed and specifying a second predetermined sequence number for performing the second set of one or more commands as part of the I/O operation; comparing the sequence numbers of the command messages received to a next expected predetermined sequence number to determine an order of performing the first set of one or more commands received relative to the second set of one or more commands received as a first execution set and a second execution set without regard to the order received; and executing the first and second execution sets in the determined order to perform the I/O operation.