Abstract: A method and system for accessing a memory subsystem from a requesting subsystem connected to a first bus. The memory subsystem is connected to a second bus. A pair of adaptors coupled to each other by a cable are respectively connected to the first and second busses. The requesting subsystem has a plurality of input/output paths from which a memory message can be transmitted to the first bus. Each such transmitted memory message includes a source code identifying the address of the requesting subsystem on the first bus and a tag bit identifying the one of the input/output paths from which the memory message is transmitted. The first adaptor has the same address on the first bus as the memory subsystem has on the second bus and receives a memory message addressed to the memory subsystem.

Abstract: A data processing system includes a plurality of data handling subsystems which communicate with each other by means of an interval transfer bus. The subsystems are located at ports along the bus and each is provided with a local bus adapter interconnecting the subsystem with the bus. Busy lines are provided, one for each port on the bus, and all such busy lines are connected to all of the ports for use by any such port when the latter is acting as a source. Each busy line is uniquely connected to an individual one of the ports and is employed at such individual port to signal to all other ports the busy or available state of the individual port. A subsystem, acting as a source, inspects the busy line that is unique to the selected destination, and if availability of the selected destination subsystem is indicated by the state of its busy line, a request for access is issued by the source, and if granted, the source raises the distination busy line to busy state, and transmits its message.

Abstract: A memory subsystem is connected to an addressable port on one bus and a non-memory subsystem is connected to an addressable port on another bus. Access to the memory is achieved by the non-memory subsystem by generating a message having a destination code indicating an address on its own bus. An inter-bus communication adapter is connected between the buses and intercepts the requesting message. The message is transmitted by the adapter while the destination code is altered to indicate the address of the memory subsystem on the other bus. The receiving memory subsystem responds by generating a response message and placing the source address into the destination address position of the message. The message is transmitted on the bus to which the memory is connected and is intercepted by a second inter-bus communications adapter. The second adapter transmits the response message to the first bus for application to the requesting subsystem.