We always get very excited when we see a new GPU architecture come down the pipe from ATI or NVIDIA. For the past few years, we've really just been seeing reworked versions of old parts. NV40 evolved from NV30, G70 was just a step up from NV40, and the same is true with ATI as well. Fundamentally, not much has changed since the introduction of DX9 class hardware. But today, G80 ushers in a new class of GPU architecture that truly surpasses everything currently on the market. Changes like this only come along once every few years, so we will be sure to savor the joy that discovering a new architecture brings, and this one is big.

These massive architecture updates generally coincide with the release of a new DirectX, and guess what we've got? Thus we begin today's review not with discussions of pixel shaders and transistors, but about DirectX and what it will mean for the next-generation of graphics hardware, including G80.

DirectX 10

There has been quite a lot of talk about what DirectX 10 will bring to the table, and what we can expect from DX10 class hardware. Well, the hardware is finally here, but much like the situation we saw with the launch of ATI's Radeon 9700 Pro, the hardware precedes the new API. In the mean time, we can only look at our shiny new hardware as it performs under DX9. Of course, we will see full DX9 support, encompassing everything we've come to know and love about the current generation of hardware.

Even though we won't get to see any of the new features of DX10 and Shader Model 4.0, the performance of G80 will shine through due to its unified shader model. This will allow developers to do more with SM3.0 and DX9 while we all wait for the transition to DX10. In the mean time we will absolutely be able to talk about what the latest installment of Microsoft's pervasive graphics API will bring to the table.

More Efficient State and Object Management

One of the major performance improvements we will see from DX10 is a reduction in overhead. Under DX9, state change and draw calls are made quite often and can generate so much overhead that the API becomes the limiting factor in performance. With DX10, we will see the addition of state objects which hold all of the state information for a given pipeline stage. There are 5 state objects in DX10: InputLayout (vertex buffer layout), Sampler, Rasterizer, DepthStencil, and Blend. These objects can quickly change all state information without multiple calls to set the state per attribute.

Constant buffers have also been added to hold data for use in shader programs.

Each shader program has access to 16 buffers of 4096 constants. Each buffer can be updated in one function call. This hugely reduces the overhead of managing a lot of input for shader programs to use. Similar to constant buffers, texture arrays are also available in order to allow for much more data to be stored for use with a shader program. 512 equally sized textures can be stored in a texture array, and each shader is allowed 128 texture arrays (as opposed to 16 textures in DX9). The combination of 8Kx8K texture sizes with all this texture storage space will offer a huge boost in texturing ability to DX10 based games and hardware.

A new construct called a "view" is being introduced in DX10 which will allow resources to be used as more than one type of thing at the same time. For instance, a pixel shader could render vertex data to a texture, and then a vertex shader could use a view to interpret the data as vertex buffer. Views will basically give developers the ability to share resources between pipeline stages more easily.

There is also an DrawAuto call which can redraw an object without having to go back out to the CPU. This combined with predicated rendering should cut down on the overhead and performance impact of large numbers of draw calls currently being used in DX9.

GPUs get Virtual Memory
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  • JarredWalton - Wednesday, November 08, 2006 - link

    They did the same thing with the original Halo, porting it (and slowing it down) to DX9. MS seems to think making Halo 2 Vista-only will get people to upgrade to the new OS. [:rolls eyes:] Reply
  • stmok - Wednesday, November 08, 2006 - link

    How else are they gonna get gamers to upgrade to Vista? :)
    (by cornering them into adopting Vista, using DirectX 10.0)

    Its sad and pathetic at the same time.

    DirectX 10.0 should be a "transitional" solution...That is, it covers both XP and Vista. This allows people to gradually upgrade their hardware, and if they wish, to Vista. What MS is doing now, is throwing everyone (developers and consumers) into the deep end, and expecting them to pay for the changes. (I suspect some would be put off by this, while the majority will continue to accept it...Which is unfortunate).


    Great article BTW. Interesting to see the high-end stuff...But I doubt I can afford it in this lifetime!

    I have two questions!

    (1) Any chance of looking at a triple video card setup?
    (I saw a presentation slide which had 2 video cards in SLI, while a third showed something else on screen).

    (2) Any idea when the GF8600-series comes?
    (mainstream market solution).
    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Great, links arent working ?

    http://www.gamedev.net/reference/programming/featu...">http://www.gamedev.net/reference/programming/featu...
    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    http://www.gamedev.net/reference/programming/featu...">

    This article was written by a friend of mine back in April after an interview with ATI. Perhaps this will clear some things up.
    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    When you break all hardware/software ties to something that has been around for 4-5 years? Its not that easy making it "transitional". From a software perspective, D3D10 is not compatable with XP in the least.

    I for one, think this is a step in the right direction.
    Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    Supposedly all of the changes to the WDDM make porting DX10 back to Windows XP "impossible", although I'm more inclined to think the correct term would be "difficult" and you also have to add in "it doesn't fit with MS marketing protocol". WDDM is quite different in Vista however, so maybe there's some substance to the claims. Reply
  • cosmotic - Wednesday, November 08, 2006 - link

    On page 9:

    --Briefly explain what a sub-pixel is in the sentence before--
    Reply
  • JarredWalton - Wednesday, November 08, 2006 - link

    Due to the size of this article and the amount of time it took to get ready, let me preempt any comments about the spelling and grammar. I am in the process of editing the final document as I read through it, and there are spelling/grammar errors. If they bother you too much, check back in an hour. If you read this an hour from now and you still find errors, then you can respond, though it would be useful to keep all responses in a single thread like this one.

    Thanks in advance,
    Jarred Walton
    Editor
    AnandTech.com
    Reply
  • xtknight - Thursday, November 16, 2006 - link

    On p 12 (gamma corrected AA):

    "This causes problems for thing like thin lines."
    Reply
  • acejj26 - Wednesday, November 08, 2006 - link

    "If DirectX 10 sounds like a great boon to software developers, the fact that DX10 will only be supported in Windows XP is certain to curb enthusiasm. "

    I believe this should say "DX10 will only be supported in Windows Vista..."

    Not to be rude, but shouldn't the article be edited BEFORE being published??
    Reply

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