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.
The 287XL is the new version of the 287. It is made in CMOS and based on the 387. It is much faster then the original.