An improved interface technique for use in a southbridge or I/O hub or in similar devices is provided where non-posted read requests are received from at least one requestor, and upstream commands based on these requests are transmitted. Response data is received in reply to commands that were previously transmitted, and responses are transmitted to the at least one requester based on the response data. A buffer unit is provided for storing command identification data that identifies commands that were already transmitted or that are still to be transmitted, and response availability data that specifies response data that has been received by the receive engine. The improvement may enable multiple outstanding read requests.