Intel 80387 is a co-processor for 80386 microprocessor family. The 80387 runs at the same speed as the 80386 and supports all execution modes of the main processor - real, protected and virtual. Being fully object-code compatible with 80287 and 8087 co-processors, the 80387 has much greater performance due to a few factors:
Higher co-processor clock frequency.
Execution of optimized FPU instructions requires fewer clock cycles.
Data bus is 32-bit.
The 80387 comes in two versions - 80387DX works with 80386DX processors, and 80387SX works with 80386SX CPUs (Since the SX and DX have different bus sizes)
This is one of the earliest versions, using CHMOS III 1.5 Micron.