Math Coprocessor Interface Evolution  From Open Watcom  Jump to:
navigation, search  Unlike many other aspects of the x86
architecture, the interface between the CPU and FPU has changed
quite significantly since the original Intel 8088/86 (and the
IBM PC). Many of these changes are invisible to software, but
not all.   Why the Changes?  Unlike the CPU, where today's CPUs
retain near-100% compatibility with the original 8088/86
processors and the differences are obscure, the x87 FPU -
originally called NDP, or Numeric Data Processor - has evolved
in incompatible ways that math libraries, and sometimes even
application software, needs to be aware of.  There were two
major driving factors of the changes. The 8087 was developed in
parallel with the IEEE 754 standard for binary floating-point
arithmetic (the IEEE 754 standard was in some ways a product of
Intel's work on the 8087). Several changes were made prior to
the final adoption of the IEEE 754, and the 287 and 387
coprocessors reflected the evolving standar