It's easy to do this experiment, and I have done in the past to prove
a point to people - I can turn the speed of the AGP interface on my
Windows box down to 4x or 2x - benchmark results are almost identical
regardless of the card - relatively modern cards like my GeForce 6800
Ultra and Radeon 9800 pro slot no perceivable drop from AGP 8x to 4x
and only a very slight drop going to AGP 2x - older cards will
probably show no difference dropping from 4x to 2x at all.
Also, the number of pipelines in a GPU has nothing to do with the
speed of the AGP interface. It's a vastly simplified description but
a chip with more pipelines will usually be faster than one with less
simply because it can process more pixel or vertex operations in a
period of time. There are other factors including the clock speed of
the GPU, the relative efficiency of performing certain operations,
the width of the memory bus, the speed of the memory and latencies at
various points in the pipeline. It's sufficient to say that the
comparison of one GPU to another is very complex, some will be good
at one kind of operation and some at another, much like a PPC970 is
good at SIMD but an Athlon64 is better at normal integer math at the
same clock. Whichever way you look at it, it has very little to do
with the interface a graphics card talks through, though if you
severely bandwidth constrain a GPU, it obviously won't be able to
receive data from the rest of the system fast enough to operate
completely efficiently (which is why there would be no point in say a
7800GTX PCI card)
Jason Mayfield-Lewis
[EMAIL PROTECTED]
If freedom is outlawed, only outlaws will be free.
On 24 Sep 2005, at 8:45 PM, pdimage wrote:
On 24/9/05 5:54 pm, "Marc van Gemert" <[EMAIL PROTECTED]> wrote:
Although on paper an AGP 8x slot is faster than AGP 4x you won't
notice the
difference in real life performance.
For example: once both my brother and I owned an AGP 8x video card
(FYI: ATi
9800XT).
The AGP slot on his motherboard was only 4x so the card ran @ AGP 4x.
On my motherboard I could ran the card @ AGP 8x.
After doing some benches I got a slightly higher score than him
(leaving out
the other hardware differences between his and mine config).
Nowadays AGP is already an old technology, PCI-Express 16x is the
new video
card slot. The first motherboards have already arrived with 2 PCI-
E 16x
slots (instead of 2x8x) for a SLI config.
But this is waaaay off-topic.
Same card in both slots is not a very good comparison for
performance -
a good comparison would be a Radeon 8500/9000/9200 in the 4x slot
compared
to the 9800XT in the 8x slot. I can put a 9200 agp in my 2x
Sawtooth and see
a fall in performance when compared to an 8500 - slower core and
memory
speed. Similarly the Radeon 9800XT will vastly outperform a 9200 or
a 8500
in my Sawtooth - but it won't outperform itself.....
PCI-E cards will vastly outperform 33mhz pci cards but you
wouldn't want
to put one in a 33mhz slot - if you could get it in - to compare the
performance it is best to compare one generation with the next. I'm
not sure
what the best 128 bit 4 pipeline 4x card was - probably the 9000
Pro - but
if you put it in a Sawtooth at 2x or a MDD with 4x I imagine the
performance
will be very similar - it's the same card.
The increase in performance derives from a combination of the next
generation slot combined with the next generation of cards built to
take
advantage of it - imho anyway....
Pete
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