A virtual machine system can run multiple conventional operating systems (OSs) in a single real host computer. A virtual machine is a logical computer with almost the same architecture as the host, and may contain several logical processors. A hypervisor is a control program to control this virtual machine system. Traditionally, the hypervisor has to receive an I/O interrupt pending for a waiting logical processor, and to simulate the I/O interrupt, consequently incurring the simulation overhead of the I/O interrupt. To avoid this overhead we present a new method which introduces a new self-wait state different from the conventional wait state, presents a new instruction for the hypervisor to detect the I/O interrupts pending for the logical processors in the self-wait state, and dispatches those logical processors on the detection ahead of the ready queue. This new method has eliminated the simulation overhead of those I/O interrupts, and enhanced the system performance to the near native.

A real storage management algorithm called Adaptive Control of Page-frame Supply (ACPS) is described. ACPS employees three strategies: prediction of the demand for real page frames, page replacement based on the prediction, and working set control. Together, these strategies constitute the real page frame allocation method, and contribute to short and stable response times in conversational processing environments.