Abstract: A computer architecture is disclosed which permits intersegment program calls with associated selective allocation of data segments of varying lengths. The calling program controls selective allocation of segments to the called program but the called program controls the lengths of the segments being allocated. In this way, recursive calls to the same program cannot affect the function or data of other programs or of the same program in a previous call. Also allocation of data segments can be postponed until execution resulting in more flexible execution of programs written without knowledge of the details of other co-executing programs.

Abstract: Secondary storage subsystems exchange messages and data with host data processing systems and also forward messages between host systems. Host systems thereby communicate with each other in addition to having access to data in subsystem storage. Access to subsystem storage is initiated by a "request" sent from a host to the subsystem. Each request is a message containing an array of one or more commands, each command specifying a transfer of data or a control function to be performed by the subsystem. A subsystem may process more than one request at a time. It also may process the commands in a request in an arbitrary sequence suited to the availability of subsystem resources and data links to host systems. After all commands in a request have been processed the subsystem transmits an associated "completion" message to the host system which originated the request. The completion message indicates the status of completion or abnormal termination of each command in the associated request.

Abstract: A high performance channel-to-channel adapter for interconnecting two or more digital computers or digital data processors. Multiple input/output device addresses are recognized by the channel-to-channel adapter. The channel-to-channel adapter makes the proper processor-to-processor connection by matching device addresses. In particular, it interconnects for data transfer purposes the two processors for which the same device address has been received. The assignment of device addresses for processor use and the direction of data transfer are by conventions agreed to among the software systems executing on the interconnected processors. The channel-to-channel adapter does not have a view of these conventions. In the more general case, two device addresses are assigned by software convention to each processor-to-processor link, one address being used to transfer data in one direction and the other address being used to transfer data in the opposite direction.