Codesigned VM

conventional VM focus on portability and functionality (to emulate differet platform), never on performance as emulating often added overhead and make execution on VM less efficient than those running on the native hardware. Codesigned VM are designed to enable innovative ISA and to improve performance or power efficency or both. In a codesigned VM,there is no native application. The VM is part of the hardware implemenation. The software portion of the codesigned VM uses a region of memory that is not visible to any system or application. This concealed memory is carved out of real memory at boot time and conventional guest software is never informed of its existence. VMM code resides in the concealed memory can take control of hardware practically any time. In the most general form, the VM software perform binary translation and cache the code in the concealed memory for execution. Hence th guest never executes directly on the native hardware. IBM AS400 uses many codesigned VM techniques. The primary objective is support for an object-oriented instruction set that redefines the hardware/softare interface in a novel fashion. The current AS400 implementation are based on an extended PowerPC ISA.