>   This is true for the *CPU*. However, it's not the CPU which handles
> the floating point code, but the FPU.
>   The FPU is completely separate from the CPU. The FPU has eight 80-bit

Well, you seems to mix CPU and ALU:
ALU stands for Arithmetic and Logic Unit. It is the part of the chip 
that compute on integers.
The ALU and the FPU are separate, but are both inside the CPU.

> registers and it performs all floating point operations on them. I don't
> know, however, if the FPU is able to load 64 and 80-bit floats directly
> from memory, but I wouldn't be surprised if it could (actually I'm not
> sure how wide the memory bus is in athlons, but I would be surprised
> if it was narrower than 64 bits).

Well, to know this for sure, we'll have to find an assembler programmer 
which will be able to say if it is possible to load one of the FPU 
register directly from the cache in the same number of cycles the other 
registers do.
If so, then the speed difference between the Athlon-XP and the Athlon-64 
is partly (they can also have improved the FPU unit...) because the last 
one can use ALL the registers to store 64 bits data, instead of the 
lower number of FPU registers and then require the cache, which is slower.

Regards,

-- 
Laurent ARTAUD (lau### [at] freefr)

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