Abstract: A technique, specifically apparatus and an accompanying method, for use in, e.g., a "host" operating system (610), for properly updating a dynamically alterable channel program that controls an input/output (I/O) device so as to emulate a "guest" computer system, that employs dynamic address translation (DAT) in an I/O channel sub-system (150), on a "host" computer system (10) that does not. This technique performs this updating in a manner that significantly increases channel throughput so as to substantially reduce a performance degradation that would otherwise result from a lack of channel DAT on the host system. Specifically, our technique relies on program controlled interrupt (PCI) chaining coupled with use of "just-in-time" translation of each new virtual channel program segment generated by a guest operating system (620) and corresponding updating of channel program (415) then executing on the host computer system.