Software Compatibility
Any software that uses only instructions supported by the P5 Pentium processor family, and that can run on that processor is considered to be Pentium compatible.
Software that uses instructions added to IA-32 after the P5 Pentium was released, and that therefore will not run on a vanilla P5 Pentium, is considered not to be Pentium compatible.
Read more about this topic: Pentium Compatible Processor