ATI Radeon HD 2900 XT: Calling a Spade a Spade
by Derek Wilson on May 14, 2007 12:04 PM EST- Posted in
- GPUs
Texturing, Caches, and Memory
Texturing
R600 features less texture hardware than we would expect to see, though AMD stands by the argument that compute power will come out on top when it matters. At the same time, we can't compute anything if we don't have any data to work with. So let's take a look at what AMD has done with their texture units.
There are four texture units in R600, one for each SIMD unit. These units don't share resources with the hardware in the SIMD units and are independently scheduled by AMD's dispatch processor. The dispatch processor is able to determine what data will be needed for threads about to execute and can handle setting up the texture units without waiting for the SIMD unit to request data and come up empty.
Texture units on the R600 are able to make both filtered and unfiltered texture requests no matter what shader is running. Unfiltered textures are useful with non-image-based texture data like vertex textures, normal maps, and generic blocks of data. Filtered requests will generally be for image data to be used in determining the color of a pixel. R600 can address one unfiltered texture per clock per texture unit and one filtered textures per clock per texture unit. Filtered units can be used to request unfiltered textures if necessary, providing an extra four unfiltered textures in place of one filtered texture.
The unfiltered texture requests will come back through four fp32 texture samplers (one per component), while the filtered requests will return 16 data points which will be run through the texture filtering hardware resulting in four filtered texture samples. The hardware can at best produce 32 single component fp16 unfiltered results per texture unit per clock. More practically, each texture unit can produce four bilinear filtered four component fp16 samples per clock alongside four unfiltered results. For textures with fp32 components, two clocks would be required to complete a bilinear filter process, as only half the data is loaded at a time to conserve bandwidth.
This is definitely a step up for R600, as R5xx hardware doesn't have texture filtering hardware for floating point textures. All told, with each of its four texture units working, R600 can consume up to 32 unfiltered textures or 16 unfiltered textures plus 16 filtered textures (as long as they're fp16 or fewer bits and we're only using bilinear filtering).
G80 is built with four texture address units and eight texture filters per block of 16 SPs. In total, this means NVIDIA's hardware can produce 32 filtered texture samples per clock (again these are fp16 and bilinear filtered). Of course, NVIDIA is operating on twice as many threads per clock, so it is conceivable that they would benefit more from having the extra filtered data.
We will have to wait and see if AMD's approach of providing unfiltered and filtered texture access in parallel pays off. For the general case on pixel shaders, we would want to see more filtered textures per clock, but with vertex and geometry shaders coming into the mix this could be a good way to save hardware space while offering more texturing power. On a final texturing note, AMD implemented "percentage closer" filter hardware for depth stencil textures. This will allow developers to implement fast soft shadows. The details of the implementation weren't indicated though.
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TA152H - Monday, May 14, 2007 - link
Fanboy? What a dork.I've had success with ATI, not with NVIDIA, and I know ATI stuff a lot better so it's just easier for me to work with. It's not an irrational like or dislike. I bought one NVIDIA and it was a nightmare. Plus, I'm not as sure they'll be around for very long as I am ATI/AMD, although they had a good quarter, and AMD surely had a dreadful one.
Selling discrete video cards alone might get a lot more difficult with the integration of CPUs, and GPUs.
yyrkoon - Monday, May 14, 2007 - link
You are a fanboy, face it. 'I tried a nVidia card once . . .' How long ago was that ? Who made the card ? Did you have it configured properly? Once?! Details like this are important, and seemily/conviently left out. Anyhow, anyone claiming that nVIdia cards are 'junk' has definate issues with assembling/configuring hardware. I say this because my current system uses a nVidia based card, and is 100% rock solid. 'Person between the chair and keyboard' rings a bell.Ask any Linux user why they refuse to use ATI cards in their system . . . You are also one of these people out there that claims ATI driver support is superior to nVIdias driver support I suppose ? If you have truely been using ATI products for 20 years, then you know ATI has one of the worst reputations on the planet for driver support(and while it may have improved, it is not as good as nVidias still).
Yeah, anyhow, ATI, and nVidia both can have problems with their hardware, it is not based 100% on their architecture, but the OEM releasing the products have a lot of effect here also. There are bad OEMs to buy from here on both sides of the fence, knowing who to stay away from, is half the work when building a PC, and probably had a lot more to do with your alleged 'bad nVIdia card', assuming you actually configured the card properly.
I also had a problem with an nVIdia card once, I bought a brand new GF3 card about 7 years ago, and a few of the older games I had, would not display properly with it. What did I do ? I waited about a month, for a new driver, and the problem was solved. I have also had issues with ATI cards, one of which drew too much power from the AGP slot, and would cause the given system to crash 1-2 times a day. This was a design issue/oversight on ATI's behalf(the card was made by Saphire, who also makes ATIs cards). What did I do ? I replaced the card with an nVIdia card, and the system has been stable since.
So you see, I too can skew things to make anyone look bad also, and in the end, it would only serve to make me look like the dork. But if you want to pay more, for less, that is perfectly fine by me.
Pirks - Monday, May 14, 2007 - link
I've got all problems and crappy drivers (especially Linux ones) only from ATI while nVidia software was always much better in my experience. power hungry noisy monsters made by whom? by ATI! as always :) same shit as with their x1800/x1900 miserable power guzzling seriesdiscrete video cards are not going away any time soon. ever heard of integrated video used in games, besides ones from 2000, like old Quake 2? no? then please continue your lovefest with ATI, but for me - it looks like I'll pass on them this time again - since Radeon 9800Pro they went downhill and continue in that direction. they MAY make a decent integrated CPU/GPU budget-oriented vendor in a future, for all those office folks playing simple 2D office games, but real stuff? nope, ATI is still out of the game for me. let's see if they manage to come back with reincarnation of R300 in future.
ironically, AMD CPUs on the other hand have best price/performance ratio, so intel won't see me as their customer. I wish ATI 3D chips were as good as AMD CPUs in that regard (and overclockers please shut up, I'm not bothering to OC my rig because I don't enjoy benchmark numbers, I enjoy REAL stuff like games, and Intel is out of the game for me as well, at least until their budget single core Conroes are out)
utube545 - Tuesday, May 22, 2007 - link
Get a clue, you fucking cretin.dragonsqrrl - Thursday, August 25, 2011 - link
haha... lol, wow. facepalm.dragonsqrrl - Thursday, August 25, 2011 - link
Damn you're a fail noob of an ATI fanboy. Time has not been kind to the HD2900XT, and now you sound more ridiculous then ever... lol.yzkbug - Monday, May 14, 2007 - link
Not a word about new AVIVO HD and digital sound features?DerekWilson - Wednesday, May 16, 2007 - link
we mentioned this ...on the r600 overview page ...
photoguy99 - Monday, May 14, 2007 - link
First to be clear and I do not condone the title of this article, there's no need to bring racism into this.But my point is NVidia can and will react by making the performance per dollar competitive for the R600 vs 8800GTS.
Once the prices are comparable, why buy a more power hungry part (the ATI)?
This is one disadvantage they can't correct until the next respin.
DrMrLordX - Monday, May 14, 2007 - link
Based on the benchmarks results, the only reason I can see for getting 2900XTs is if a). you don't care about power consumption and b). want to run a Crossfire rig at a lower cost of entry than dual-8800 GTXs or 8800 Ultras.As others have said, some more benchmarks in mature DX10 titles might show who the real winner here is performance-wise, and that holds true for multi-GPU scenarios as well.