A method, computer program product and computer system that features intermittently entering the system management mode of a processor to commence and terminate I/O activity between external devices and computer system resources. To that end, a system management interrupt handler is included that monitors bus transactions between a bus controller and an external device that is the subject of I/O activity. Upon sensing the completion of a bus transaction, the system management interrupt handler transmits a system management interrupt to the processor. In response thereto, the processor reads a buffer in the bus controller and provides the requisite resources with the I/O information contained therein.