[geeks] examples of vector processors (vs scalar

[Joshua D Boyd]

On Mon, Aug 05, 2002 at 05:18:41PM -0400, dave at cca.org wrote:
> jdboyd at cs.millersville.edu writes:
> 
> >Now (and this is from listening to others, rather than personal
> >experience), Altivec allows adding 2 sets of 4 floats in one instruction
> >like above (this part I know personally from reading the docs, and
> >reviewing OS X code that used the units).  Cray's (and here is where I
> >get to the hear say) can add 2 sets of 4 floats together like that one
> >instruction, but they can also add a 2 sets of a few hundred floats
> >together in one instruction as well.
> 
> If I understand the Crays correctly, the fact that one instruction
> operates on a large array does *not* mean that all the elements
> are actually calculated simultaneously. It's actually just a
> really really optimized loop, initiated by a single instruction.
> Obviously that lets you tune the hardware to keep all the stages
> of the pipeline running optimally, but it isn't what would be called
> "SIMD" in the MPP world.

Good point.

-- 
Joshua D. Boyd