Intel 80387SX
The Intel 80387SX (387SX or i387SX) is the math coprocessor for the Intel 80386SX microprocessor. It was used to perform floating point arithmetic operations directly in hardware. The coprocessor was designed only to work with the SX variant of the i386, rather than the standard 80386. This was because of the 80386SX's 16 bit data bus, which was modified from the original i386's 32 bit data bus.