X-bit labs

ATI RADEON X700 XT: Architecture Preview (page 2)

Category: Video

by Alexey Stepin , Tim Tscheblockov, Anton Shilov

[ 09/21/2004 | 04:54 AM ]

RADEON X700: First Look at the New GPU

Unlike its elder brother X800, the RADEON X700 is manufactured with a thinner 0.11-micron tech process, which did well in the low-end ATI RADEON X300 processor. The RV410 chip consists of about 110 million transistors – much less than in the NV43 and slightly less than in the RADEON 9800 XT. The use of the new technological process usually leads to higher clock rates and a lower heat dissipation level; coupled with the relatively low transistor count it also potentially reduces the cost of the graphics chip. We’ll find out shortly if any of these truths applies to the X700, but now we are going to examine closely the architectural specifics of the chip.

Like any other PCI Express product from ATI, the RADEON X700 features native support of this new peripheral bus (as you know, this interface is realized through a special bridge in chips of the GeForce PCX and the GeForce 6800 families). The foundation of the new GPU is formed by the successful X800 architecture with all its features: 3Dc, SMOOTHVISION HD, SmartShader HD, VideoShader HD, HyperZ HD, to mention a few. You can refer to our review of the RADEON X800 series for a detailed description of these technologies.

The X700 comes without support of Shader Model 3.0, but of course can execute pixel shaders of version 2.0b. Thus, NVIDIA retains its technological leadership as concerns executing pixel shaders. Anyway, game developers are not rushing yet to add this shader model into their products, and we doubt they will change their attitude in the near future.

As mentioned above, the X700 resembles the X800, but has fewer pixel pipelines (eight) and a narrower memory bus (128 bits). Instead, ATI equipped its new mainstream GPU with six vertex processors, like in the more expensive chips from both ATI and NVIDIA. This is twice the number of vertex processors of the GeForce 6600 chip!

So, the RADEON X700 communicates with GDDR3 memory across a 128-bit bus, like its market rival, the GeForce 6600, does and this narrow bus may become the bottleneck in high resolutions and/or with full-screen antialiasing. The use of a 128-bit bus and fast memory is, however, justifiable with respect to mainstream graphics cards: the price of the fast memory chips, which must be used to ensure a higher memory bandwidth, is going to decrease, while the price of the complex PCB and the die packaging, necessary to realize a 256-bit bus, is going to remain at the same high level throughout the lifecycle of the product.

By the way, the company offers three flavors of the X700: RADEON X700 XT, RADEON X700 PRO and RADEON X700. They only differ in the clock rates and the memory amount, though:

The cards will have all the connectors you’d expect them to have: DVI-I, D-Sub and S-Video. Interestingly, the XT and PRO models have the same recommended price, so we will have a choice between a faster graphics card with less of memory and a slower graphics card with a double memory amount. The price being equal, the RADEON X700 XT seems preferable between the two, though, as 128MB of graphics memory is quite enough for almost any application today. The RADEON X700 PRO is unlikely to be shipped with expensive and fast GDDR3 memory, so it won’t probably overclock to the frequencies of the X700 XT. On the other hand, the PCB design of the RADEON X700 XT and X700 PRO is identical, so some graphics card manufacturers may put 256MB of memory on board of their versions of the RADEON X700 XT unless ATI objects to such actions of its partners.

The new family of mainstream GPUs that should press the RADEON X600 family down and become a PCI Express alternative to the RADEON 9800 XT looks good at the first approach, save for the narrow memory bus. We are going to see soon if this 128-bit bus has any negative impact on the performance.