It's bullshit, the C94 had a peak of 4GFLOPS (double precision, which
the Xbox certainly can't match).
The XBox has a peak of 733MFlops double precision, or just shy of
3Gflops single precision in the CPU (SSE boost single precision
performance a lot, but the chip doesn't support SSE2, so no double
precision).
The 80 gigaflops number is, as you mentioned, complete bullshit. It's
all from the GPU, which can't be used for general purpose programming.
It also can't do double precision, and it definitely does not even
have 80GFlops peak even if it could do all of those things.
The GPU of the XBox runs at 233MHz and has 4 pipelines. Therefore, to
get the 80GFlop number, nVidia is saying that each pipeline can do 85
floating point instructions at a time. I have absolutely no idea how
they managed to get such a ridiculous number, but it has absolutely no
bearing on reality.
At an absolute maximum you're looking at 233MHz x 4 pipelines, each
capable of handling 4 chunks of single precision data at a time
(128-bit wide vector) and maybe being able to do two flops at once (eg
a multiply-add). That would give you some sort of theoretical maximum
of 7.4 GFlops. Of course, the real number is actually zero flops
since it's not programmable. Also there is no possibility of doing
any double precision on this, so it gets a fat 0 GFLops there.
In any case, end result is that the total processing umph of the XBox
CPU+GPU is a theoretical 10 GFlops of single precision, or 0.73 GFlops
double precision. The PS2 gets 6.4GFLops single percision and almost
nothing double precision.
The C94 does 35GB/s on STREAM TRIAD,
I'd be surprised if the Xbox can do 3GB/s.
XBox has 400MT/s memory (200MHz DDR) with a 128-bit interface. Max
theoretical bandwidth is 6.4GB/s. But most of that bandwidth goes to
the graphics processor (makes sense, that's where the bandwidth is
needed). Max theoretical bandwidth to the CPU is 133MT/s and 64-bit,
or 1.06GB/s. If you could run some sort of STREAM TRIAD on the GPU,
it could probably get well over 3GB/s, but on the CPU you aren't even
going to hit 1GB/s.
And the C94 is from 1991...
Err, wasn't it from 1994? Hence the 'C94' name? Still hardly a
current product.