AVM/EF (Advanced Virtual Machine/Extended Facilities) was an operating system (hereinafter “OS”) that controlled Fujitsu’s virtual computer (VM: Virtual Machine) system. It was announced in June 1982. AVM/EF achieved a small, 5 to 15% overhead (increase ratio of the CPU time of the real computer to the CPU time on a virtual computer) by using a high-speed VM mechanism in the hardware, and provided a high-performance virtual computer system. In June 1989, AVM/EX (Advanced Virtual Machine/Extended) was announced. AVM/EX used an extended VM mechanism that harmonized with the new architecture EXA (EXtended Architecture) of the M series, and reduced the overhead to as little as 1/3 of that of AVM/EF.