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2. Partial processor emulation - If the target architecture is a newer or more advanced version of the host architecture, it is possible to execute most instructions directly on the host processor. An instruction which is not supported by the host will cause an exception (like a software interrupt) which would normally cause the process to be aborted. In partial processor emulation, the emulator handles the exception, processing the unsupported instruction using software emulation, and then returning control to the CPU. This is much faster than full processor emulation, because the majority of instructions are handled directly by the CPU. The performance varies according to the ratio of instructions which may be directly executed to instructions which must be handled in emulation.
Both of these techniques may be used in a virtual machine (VM), which simulates a full standalone computerof the emulated architecture, or for userspace emulation, which supports one a specific processes (and possibly child processes) which on a system which is otherwise natively running on the host system(for example, running an aarch64 process on a system which is otherwise running x86_64 processes).
The [https://www.qemu.org/ QEMU] project provides a range of high-quality emulators and virtualizers based on these two technologies.
