If there's one buzzword you'll be hearing a lot about as ATI's DirectX 10 hardware nears release, unified shading will probably be it. Of course, this won't be the first time we've seen an architecture using unified shaders, as of course ATI have already leveraged such a design to good effect on the 'Xenos' GPU used in Microsoft's Xbox 360, a point they are keen to point out as evidence that they know what they're doing when it comes to this stuff.

So, what are unified shaders all about? As a principle, it's actually pretty simple. Take a look 'inside' a current PC graphics architecture, be it from NVIDIA and ATI, and you'll find very distinct units within it, two of which you should already be somewhat familiar with in the form of vertex and pixel shaders. To quickly clarify the functionality of these units, vertex shaders deal with the manipulation of geometry in a scene by way of small sets of instructions telling the shader units what to do to particular vertices, while pixel shaders also accept instructions, but instead apply this code to pixels rather than vertices.

While the shift from DirectX 9 to 10 isn't going to be as large as that from 8.1 to 9, it's still enough to get the 3D hardware geek juices flowing at least somewhat, and is another incremental step on the way to truly realistic and immersive in-game 3D environments. As ever, the biggest question is when we'll be seeing the new functionality of DirectX 10 put to good use? These things take time for developers to get to grips with and integrate into games, so doubtless it'll be a year after the APIs release at least before we start to see what could be called 'true' DirectX 10 content. The uptake of new functionality, the use of geometry shaders in particular, will also be dependant on the speed of first-generation hardware at processing these effects of course - In the aforementioned example, I've already heard rumours of poor performance from one IHVs DirectX 10 part, which suggests that we might not see geometry shaders used 'in anger' for quite some time. As ever, time will tell.

As far as unified shaders go, moving to this kind of architecture certainly seems to be more a case of 'when' rather than 'if' on the part of all the graphics vendors, but it seems that as things stand, ATI are leading the way in this sense. Will this give them an advantage? Again, we'll have to wait and see.