PR/SM
In mainframe computing PR/SM (Processor Resource/System Manager) is a type-1 Hypervisor (a virtual machine monitor) that allows multiple logical partitions to share physical resources such as CPUs, I/O channels and LAN interfaces; when sharing channels, the LPARs can share I/O devices such as direct access storage devices (DASD).  PR/SM is integrated with all IBM System z machines. Similar facilities exist on the IBM Power Systems family, and its predecessors.

IBM introduced PR/SM in 1988 with the IBM 3090 processors.

IBM developed the concept of hypervisors in their CP-40 and CP-67, and in 1972 provided it for the S/370 as Virtual Machine Facility/370. IBM introduced the Start Interpretive Execution (SIE) instruction as part of 370-XA on the 3081, and VM/XA versions of VM to exploit it. PR/SM is a type-1 Hypervisor based on the CP component of VM/XA that runs directly on the machine level and allocates system resources across LPARs to share physical resources. It is a standard feature on IBM Z and IBM LinuxONE machines.

IBM introduced a related, simplified, optional feature called Dynamic Partition Manager (DPM) on its IBM z13 and first generation IBM LinuxONE machines. DPM provides Web-based user interfaces for many LPAR-related configuration and monitoring tasks.

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References

Virtualization software
IBM mainframe technology