Abstract: The embodiment discloses a method and means for partitioning the resources in a data processing system into a plurality of logical partitions. Host control code may be embodied in programming, microcode, or by special hardware to enable highly efficient operation of a plurality of preferred guest programming systems in the different partitions of the system. The main storage, expanded storage, the channel, and subchannel resources of a system are assigned to the different logical partitions in the system to enable a plurality of preferred guest programming systems to run simultaneously in the different partitions. This invention automatically relocates the absolute addresses of the I/O channel and subchannel resources in the system to their assigned partitions. Also the absolute and virtual addresses of the different guest programming systems are relocated into, as well as page addresses for any expanded storage, their assigned partitions.

Abstract: The embodiment obtains rapid switching between system control programs (SCPs) by switching an address in a prefix register in a CPU of a MP or UP data processing system from a guest SCP's PSA (program save area) to a host SCP's PSA by fetching the host prefix value from a predetermined control block in main storage. The prefix register loading changes the control of the CPU from a preferred guest SCP to a host SCP. This SCP switching is done by hardware and/or microcode means in the CPU. It further detects preset states in the CPU that enable a rapid determination of which SCP is to handle a sensed event, permitting the guest SCP to immediately handle events predetermined to belong to the guest. This manner of CPU control obtains for a preferred guest SCP (such as MVS/370) operating under a host SCP (such as VM/370) nearly the efficiency of standalone execution on the CPU by the preferred guest SCP.