Hooked On Composite, Need New GPU

[Lennart Sorensen]

On Wed, Dec 20, 2006 at 07:21:18AM -0500, JoeHill wrote:
> Ways back, I believe it was Jamon, who had a GF...something that I missed
> snagging.
> 
> I think someone (Lennart? Musta been, he knows everything ;-)) mentioned what I
> should be looking at for price/performance was a GF 6200? It would obviously
> need to have 256MB or vram, and my aim is to be able to play Quake 4 and Doom 3
> (I can play that on my current GF4 Ti, but at 640x480 with half the effects
> turned off).

I just got a 7600GT (slightly overclocked from the maker) made by XFX
for the machine I built for my sister last weekend.  Rather nice
performance, and should work fine under linux too (although my sister
runs XP).  Of course this assumes you use PCIe and not AGP.

When comparing GPUs there are a number of things that matter:
Memory quantity: For some programs having lots of memory helps it do
better quality or sometimes better performance.  It is probably the
least important for performance in general though.

Memory buswidth: Some cards are 64bit, some 128bit, some 256bit, and on
8800 cards, they have 320 or 384bit.  Wider bus means more data per
clock transfered.  Two cards with the same memory clock with one using
128bit and the other 256 bit, well the memory speed of the 256bit is
twice as high.  Many budget cards used to use a 64bit version of a chip
that was normally 128bit to cut costs, and of course seriously impacted
performance too.

Memory clock: Faster memory clock means more transfers per second which
means more textures can be read, more pixels generated, etc.  Memory
speed is important.

GPU clock: The higher the clock rate the more operations the GPU can get
done.

Pipelines: The more pixel pipelines you have, and the more textures can
be applied per pass by a pipeline, the more pixels can be generated per
clock.  A card with 12 pixel pipelines will run much faster than one
with 8 pipelines, if they run at the same clock rate.  The pipeline
count is usually one of the major differences between GPUs in the same
family.  Quite often lower end models are higher end models with
defective pipelines that were disabled at the factory.  Not always but
often.  On some older cards you were sometimes able to reenable some of
the disabled pipelines, if you for some reason thought your card might
have a good chip that was just downgraded to produce a cheaper model
chip.

So basicly: 
Memory bandwidth = memory clock * memory buswidth
Pixel bandwidth = gpu clock * pixel pipelines

It is over simplified since some newer chips have more efficient
pipelines, and some can do antialiasing with almost no performance hit
while older ones had major performance hits, etc.

I tend to go to this page to compare nvidia GPUs (since I don't buy any
other kind):
http://en.wikipedia.org/wiki/Comparison_of_NVIDIA_Graphics_Processing_Units

So for example it shows that a GF6200 has a fill rate of 1200MT/s (1200
million textured pixels per second) and a memory bandwidth of either 3.2
or 6.4 GB/s (depending on whether it is a 64 or 128bit memory bus
version of the chip.  Good luck finding that in the specs on the box,
although it is rather important to know).

A 7300GT (the GS uses turbocache aka it uses some system ram to help
its pathetic amount onboard) on the other hand has a fill rate of
2800MT/s and a memory bandwidth of 10.67GB/s.  It would be a lot faster
than a 6200, and probably not that different in price.

A 7600GT gets to 6720MT/s and a memory speed of 22.4GB/s on a normally
clocked card.  The XFX card I picked up (for about $20 more than a
normally clocked card which was VGA/DVI rather than the dual DVI I
wanted) runs at 7080MT/s and a memory speed of 25.6GB/s.

Using the MT/s and GB/s as a rought guide to speed of different models
is pretty good, although not a perfect measure.

> Any suggestions as to a good source/store (I'd like, if possible, to avoid Best
> Buy and that), esp if it's in the West end? Or anyone else got one they wanna
> offload?

www.canadacomputers.com (lots of locations in the GTA and hard to beat
prices.  Even www.logiccomputerhouse.com can't match their prices
anymore.)

--
Len Sorensen
--
The Toronto Linux Users Group.      Meetings: http://gtalug.org/
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://gtalug.org/wiki/Mailing_lists