Thorsten Froehlich <tho### [at] trfde> wrote:
> For two decades now the CPU and FPU have been the same thing on x86. It is 
> not like they are two different processors. They are *one* processor. The 
> terminology is just a leftover from times when the logic we nowadays call 
> FPU did not fit on the same die as the integer unit called CPU back then.

  That doesn't matter. The CPU part does not stop if the FPU is doing
something (the only situation where the CPU will wait for the FPU is
when it tries to retrieve some value from it).

  This means that if the program executes an FPU opcode which takes dozens
of clock cycles for the FPU to perform, the CPU part will continue executing
CPU opcodes until a new FPU opcode (eg. fst) is encountered.

  The original Quake engine was rather famous for using this to its
adantage in the 486 and Pentium processors: While FPU was calculating
a heavy division (heavier in those days than today), the CPU was
interpolating and drawing textures linearly the next 15 pixels. This
made the division operation almost free (at the cost of the perspective
correctness of the texture not being completely perfect).

-- 
                                                          - Warp

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