RV670 in 55nm
As much as AMD is very conservative in its fabrication processes for its CPUs, the firm is aggressive on the very latest manufacturing processes offered by TSMC for the production of its GPUs. Thus, the RV670 which equips the Radeon HD 3800 ushers in the 55 nanometer process. As they usually do, after 65 nanometers TSMC proposes a "half node" process which means an intermediate technology between two methods of production. The 55 nanometer is therefore based on their 65 nanometer technology but updated for finer engraving.
As usual, the interest here is to lower production costs as well as power use – a point upon which AMD strongly insists.
The RV670 can be seen as an R600 (Radeon HD 2900 XT) which is more efficient in terms of its design. In this way, the RV670 inherits the R600’s entire shader core, in other words, 64 vec5 units to process shaders (AMD speaks of 320 scalar processors as Nivdia does, which in actuality isn’t too accurate) and 16 texturing units. You can take a look at our article on the Radeon HD 2900 XT to brush up on the details.
So what is different? Mainly the memory bus which is now reduced to 256 bits instead of the R600’s 512 bit. Next, there is the (supposed) improvement of the ROPs which is only normal given that it seems obvious that those of the R600 suffered from certain problems which limited performances with antialiasing. AMD always denied a problem of this type responding that they opted for more flexibility from the start. However you'll probably agree with us that voluntarily choosing to kill a GPU’s performances in an area that always put the Radeon brand ahead seems a bit unlikely. Whatever the case, we can assume AMD worked on this point resulting is some compensation for the reduction in bus width.
There are a few innovations. First of all, there is PCI Express 2.0 whose interest is yet to be proven even if AMD announces gains of 10% on the Radeon HD 3850 256 MB version. Next, there is UVD on a high performance card. And finally, AMD’s Radeon HD 3800 is the first card to support DirectX 10.1.
In the end, the 55 nanometer RV670 should be almost equivalent to an R600 (80 nanometers) while having 34 million transistors less (666 versus 700 million) and being half its size. Indeed, the RV670 only measures 192 mm² versus 408 mm² for the R600! This is quite an improvement and something that should allow AMD to be more aggressive on prices.
DirectX 10.1
This light evolution of DirectX 10, like the shader model 3.0 introduced by DirectX 9.0c is an important argument for AMD because it’s the first to offer its support. DirectX 10.1 and shader 4.1 add small improvements in different areas by correcting deficiencies of the first version of DirectX 10, adding a little more flexibility and bringing control of antialiasing to developers. If you are interested in the details, here they are:
So is DirectX 10.1 support important today? It’s definitely a bonus, but at the same time developers are only starting to use DirectX 10 and will not be able to take advantage of this update for some time. This is all the more true given that we will have to wait for the SP1 of Windows Vista to see its appearance.
Of course, Nvidia is loudly proclaiming that DirectX 10.1 is useless. However, the contrary would have been surprising because they are late in its integration to their GPUs. DirectX 9.0c was THE revolution, but DirectX 10.1 is without interest. As usual, the reality is somewhere in between. However, in the GeForce 8800 GT’s presentation this manufacturer managed to have the head of Microsoft’s gaming division affirm quite resolutely that the update of this API would be useless, almost anticipating the arrival of its support for AMD. A good dose of hypocrisy for Microsoft…
Whatever the case, it’s obvious we will have to wait to see if developers take interest before it will become a large advantage. In the meantime, this is still a positive point.
