1. In a data processing system including a main processor and at least one input/output device connected to a bus, the improvement for configuring said system to allow the addition of a co-processor to operate concurrently with said main processor and selectively sharing utilization of said input/output device, comprising: means dynamically controlled by said main processor for selectively preventing direct access to said input/output device in response to an attempted access by said co-processor; means connected to said means for selectively preventing for utilizing said main processor to service said attempted access of said input/output device by said co-processor when said means for selectively preventing has been enabled to prevent direct access to said input/output device by said co-processor; and said means for selectively preventing and said main processor allowing concurrent utilization of said input/output device by said main processor and co-processor when said means for selectively preventing has not been enabled.