AMD P80C287 -10

This a co-processor (FPU; for floating point calculations) for the 80286 processors. It's similar but not pin-compatible to the 8087. The number of instructions and execution time of instructions is practically identical with the 80287 compared to the 8087. The main difference between the 80287 and 8087 is the way how the CPU communicates / interfaces with the co-processor.

You can run a 10MHz 80287 FPU with a 12MHz CPU. This is because the CPU divides the base clock by 1/2 and the FPU by 1/3 meaning that the FPU always runs a few MHz slower.