Technical solutions are described for computing data check word for a host request for an I/O processing operation at a host computer system that communicates with a control unit. An example method includes obtaining information for a first I/O operation at a channel subsystem in the host computer system, and accessing an address control word (ACW) of the first I/O operation. The ACW is stored in the local channel memory, and the ACW includes a first data check seed-value. The method also includes computing a first data check word based on the first data check seed-value from the ACW. The method also includes obtaining information for a second I/O operation at the channel subsystem, and in response to the second i/o operation corresponding to said ACW of the first I/O operation, computing a second data check word based on a second data check seed-value from a cache memory.