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.
[1] A programmer who wishes to use a supplementary feature of a CPU is faced with a couple of choices.
[2] Some popular processor architectures such as x86, 68000, and MIPS have seen many new capabilities introduced over several generations of design.
Some of these capabilities have then seen widespread adoption by programmers, spurring consumer upgrades and making the previous generations of processors obsolete.
Programs containing these instructions may not operate correctly on all machines in the IA-32 family: The FPU (Floating Point Unit) maths co-processing capability is available on all x86 processors since the 80486DX series.