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 Post subject: What's keeping DX10 Cards from running DX11?
PostPosted: Fri Aug 17, 2012 7:32 pm 
Folding for Elena
Folding for Elena
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I'm just wondering if it would be possible for someone to come up with software/firmware allowing dx10/10.1 cards, like the 4870 and GTX270 to run DX11. Is it a limitation of the cards' respective firmware, or it is actually a hardware limitation. I'm asking because I feel like the cards would be powerful enough to compete with low-midrange gaming cards out currently, if only they were capable of running DX11.

Thanks in advance for answering
-Josh


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Fri Aug 17, 2012 10:40 pm 
Smithfield
Smithfield

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Because DirectX 10 cards don't have tessellations engines.

High level architecture of NVIDIA's G80 GPU
Architecture for GF110

Of course, you could run it in software in the graphics pipeline, but you'll incur a rendering penalty that would make running DirectX11 on DirectX10 cards worthless. Besides, the GTX 460 1GB beats the GTX 285, and the GTX285 still goes for a hefty price tag of at least $250 if you can find it while a GTX 460 goes for as little as $150. So there's no point.


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Sat Aug 18, 2012 3:10 pm 
Folding for Elena
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So there is an actual hardware difference from dx10 cards to dx11 cards. huh.

And you're absolutely correct about the price discrepancies, I was only wondering because I currently have a 4870, and was wondering if it would even be remotely possible/fruitful to look into.


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Sat Aug 18, 2012 3:19 pm 
Smithfield
Smithfield

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Well, here's another thing however. The Radeon HD 3000-4000 cards do have tessellation engines. However, they don't work with DirectX and it's probably doubtful any game actually uses it. So not only do DX10 cards may lack a tessellation engine, but it won't conform to DirectX.

Of course we could ask why the hell does it matter. Because having a standard is good. There were plenty of features on video cards that were just released on DirectX 10 and 11, such as geometry instancing (this has been on the Radeon 9800 cards) and order-independent transparency (Been around on PowerVR cards, since 2001). But the problem is that these features are specific to those cards, with their own implementation. If you don't have a standard, then games developers won't use it because their code base will be more complicated. Not to mention these are really "nice to have" features.


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Mon Aug 20, 2012 5:26 am 
Folding for Elena
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So basically, in order to have a card compatible with DX, you have to conform to all of the specifications, one of those being a specific type of tessellation engine, which is not the type used in the 4--- series Ati cards.

And to be clear, the differences between the 4--- series style of tessellation engines and DX11 compatible engines is too great to be overcome by software, correct?


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Mon Aug 20, 2012 6:46 am 
Smithfield
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It's really up in the air whether AMD tweaked the 4000 series tessellation engine for DirectX 11 or they didn't have to do a thing and DirectX 11 merely required having one.

So let me back up since I may be confusing myself and you. DirectX has a list of hardware specifications that the manufacturer must meet in order to be DirectX complaint. As far as I can gather between major versions:

  • DirectX 6 wasn't any thing fancy other than optimizations for CPU instructions (x87, MMX, 3DNow!) and texture format support
  • DirectX 7 required transform and lighting on the hardware itself.
  • DirectX 8 required the hardware to allow for programmable vertex and pixel shaders.
  • DirectX 9 was weird, but the hardware had to support high level shader languages, multiple render targets (a requirement for deferred shading), and floating point texture formats (required for HDR rendering). 9.0a was optimized for NVIDIA's implementation for 16-bit floating point textures. 9.0b was more for ATI and their 24-bit implementation (although DirectX 9 required 24-bit floating point in the first place...). 9.0c just tweaked with the parameters on shaders.
  • DirectX 10 required a geometry shader as well as unified resource allocation. I suppose in light of this, hardware manufacturers took the route they did, instead of what AMD did with the Xbox 360 GPU (which superficially looks like an X1800, just with a unified pipeline). Wikipedia says there's also "Instancing 2.0", which suggests that DirectX 9 had it.
  • DirectX 11 required a tessellator and support for compute shading.


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 Post subject: Re: What's keeping DX10 Cards from running DX11?
PostPosted: Mon Aug 20, 2012 10:53 am 
Folding for Elena
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That makes sense. I've been reading up on this subject outside these forums as well, and have discovered that while the 4870 supports a lot of the things necessary to run DX11, it doesn't support all of them, making it totally incompatible. Kind of a bummer, but it sheds some light onto why AMD discontinued support for everything series 4xxx and older.


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