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The Intel80287 (i287) was the math coprocessor for the Intel 80286 series of microprocessors. It was used to perform floating point arithmetic operations directly in hardware and normally ran at two thirds the speed of the 286 CPU. Intel (and its competitors) later introduced an 80287XL, which was actually an 80387SX with a 287 pinout. The 80287XL contained an internal 3/2 multiplier so that motherboards which ran the coprocessor at 2/3 CPU speed could instead run the FPU at the same speed of the CPU.
The 80287 and 80287XL also worked with the 80386 microprocessor, and was initially the only coprocessor available for the 80386 until the introduction of the 80387 in 1987. Finally, it was also able to work with the Cyrix Cx486SLC. However for both of these chips the 80387 was strongly preferred for performance reasons and the greater capability of the instruction set.
