Intel 80287 is a co-processor for 80286 family of processors. The 80287 has architecture similar to Intel 8087, and it's completely object-code compatible with the 8087 (but not pin- compatible). The number of instructions and execution time of instructions for both co- processors is about the same. There are some differences between the 80287 and 8087 FPUs:
The 80287 may run asynchronously from the main processor. The 80286 processor divides external clock by 2, while the co-processor divides it by 3. If both the 80286 and 80287 use the same external clock it results in the co-processor running at the 2/3 speed of the main processor.
When the main processor executes the FP instructions it now checks if the co-processor is busy, and, if necessary, will wait for the co- processor to become available. As a result, it's no longer necessary to add WAIT (FWAIT) instruction before most of the 80287 instructions.
The Intel 80287 was produced at speeds ranging from 5 to 12 MHz. Other companies produced 16 MHz and 20 MHz versions of the FPU. AMD, Cyrix, and IIT also made 287's.