An interbus interface module enables storage and transfer of commands, messages and data between parallel a dual system bus operating on a first protocol and a subrequestor bus operating on a second protocol. The interface module serves a first group of requestors, such as multiple processors and main memory, for handling data transfers to and from the subrequestor bus via said dual system buses while also handling data transfers to and from a second group of requestors connected to the subrequestor bus.