64-bit CPU

[Lennart Sorensen]

On Thu, Sep 16, 2004 at 04:40:40PM -0400, Andrej Marjan wrote:
> I know that was the intent of MMX. I had just (incorrectly) assumed that 
> since they had gone to the trouble of overloading the floating point 
> registers to allow for integer arithmetic, they would have gone the 
> extra step of allowing arithmetic on the full 64 bits as a single entity.

Remember the industry in general found MMX useless, but the extra L1
cache did speed things up in general.  I think full 64bit integer
operations would have been useful to have.

> Well... considering that MMX was just grafted onto a ppro core, it would 
> be less invasive (and cheaper) to just reuse the only registers that 
> were big enough for the new purpose...

MMX was first grafted onto the P5 core as the Pentium MMX (166, 200 and
233MHz, which also had twice the L1 cache of the original Pentium I
believe).  When the Pentium II came out later it added MMX to the P6
core.  The Pentium Pro never had it as far as I know (at least not the
steppings of the PPro I ever used).

Lennart Sorensen
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