supplementary

A processor supplementary capability is a feature that has been added to an existing central processing unit (CPU) design after the initial introduction of that design to the marketplace.
A supplementary capability increases the usefulness of the processor design, allowing it to compete more favorably with competitors and giving consumers a reason to upgrade, while retaining backwards compatibility with the original design.
The CPU supplementary instruction capability does not as a rule apply to 8 or 16 bit CPUs, as many of these CPUs are used mostly as microcontrollers. On modern 32 and 64 bit CPUs the processor supplementary capability does not extend to Floating Point Units (FPUs) or Memory Management Units (MMUs) as these are considered to be fundamental core functionalities. Extensions to the core functionalities of the MMU and FPU may be considered CPU extensions however.

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