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Pixel-filling power
We'll begin our testing with a quick look at some theoretical numbers for pixel throughput. These numbers are mainly related to the card's ability to push pixels through the traditional graphics pipeline, and they are becoming increasingly less important as programmable shading becomes more prevalent. They are still relevant in many of today's games, though, so we'll have a quick look at them. I've included the Radeon X1300 XT and Radeon X1650 Pro in the table below for reference, even though we don't yet have examples of those cards to test.

  Core
clock
(MHz)
Pixels/
clock
Peak
fill rate
(Mpixels/s)
Textures/
clock
Peak
fill rate
(Mtexels/s)
Effective
memory
clock (MHz)
Memory
bus width
(bits)
Peak memory
bandwidth
(GB/s)
Radeon X1300 XT500420004200080012812.8
Radeon X1600 XT5904236042360138012822.1
Radeon X1650 Pro6004240042400140012822.4
Radeon X1800 GTO500126000126000100025632.0
GeForce 7600 GT56084480126720140012822.4
GeForce 7800 GT400166400208000100025632.0
All-In-Wonder X190050016800016800096025630.7
Radeon X1800 XL500168000168000100025632.0
Radeon X1800 XT62516100001610000150025648.0
Radeon X1900 XT62516100001610000145025646.4
GeForce 7800 GTX4301668802410320120025638.4
Radeon X1900 XTX65016104001610400155025649.6
Radeon X1950 XTX65016104001610400200025664.0
GeForce 7900 GT4501672002410800132025642.2
GeForce 7800 GTX 5125501688002413200170025654.4
GeForce 7900 GTX65016104002415600160025651.2
GeForce 7950 GX22 * 5003216000482400012002 * 25676.8

The Radeon X1900 XT 256MB has the same basic specs as the 512MB version, save for memory size. That puts it in a very respectable place. The X1950 XTX, meanwhile, has a tremendous memory bandwidth advantage on everything but the "SLI on a stick" dual-GPU GeForce 7950 GX2.

How do these numbers translate into performance on synthetic fill rate benchmarks?

The X1950 XTX's faster RAM helps it make big gains over the Radeon X1900 XTX in the single-textured fill rate test, despite having the same GPU clock frequency. Once we get into multitextured pixels, though, that advantage is muted.

Of course, these numbers aren't destiny in real-world applications. The GeForce cards do especially well here thanks to their ability to use one of the ALUs in each of their pixel shader processors for texturing. The R580-derived cards, meanwhile, have 16 dedicated texture address units and 48 dedicated pixel shader processors at their disposal. In other words, the two architectures allocate their resources quite differently, and the implications are difficult to predict with a simple fill rate test.