Compare any two graphics cards:
GeForce GTX 580 3GB vs Radeon HD 6950
IntroThe GeForce GTX 580 3GB comes with a GPU core clock speed of 772 MHz, and the 3072 MB of GDDR5 memory runs at 1002 MHz through a 384-bit bus. It also is comprised of 512 SPUs, 64 TAUs, and 48 ROPs.
Compare those specs to the Radeon HD 6950, which has a GPU core clock speed of 800 MHz, and 1024 MB of GDDR5 RAM running at 1250 MHz through a 256-bit bus. It also features 1408 Stream Processors, 88 TAUs, and 32 ROPs.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
As far as performance goes, the GeForce GTX 580 3GB should in theory be a small bit better than the Radeon HD 6950 in general. (explain)
Texel RateThe Radeon HD 6950 should be a lot (about 42%) better at AF than the GeForce GTX 580 3GB. (explain)
Pixel RateIf running with lots of anti-aliasing is important to you, then the GeForce GTX 580 3GB is superior to the Radeon HD 6950, and very much so. (explain)
Please note that the above 'benchmarks' are all just theoretical - the results were calculated based on the card's specifications, and real-world performance may (and probably will) vary at least a bit.
Memory Bandwidth: Bandwidth is the max amount of information (counted in megabytes per second) that can be transferred over the external memory interface in a second. It's worked out by multiplying the interface width by its memory speed. If the card has DDR RAM, the result should be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The higher the card's memory bandwidth, the better the card will be in general. It especially helps with AA, HDR and high resolutions.
Texel Rate: Texel rate is the maximum number of texture map elements (texels) that are processed per second. This number is calculated by multiplying the total amount of texture units of the card by the core clock speed of the chip. The better the texel rate, the better the video card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed in one second.
Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics card can possibly write to the local memory per second - measured in millions of pixels per second. The figure is calculated by multiplying the number of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel output rate also depends on lots of other factors, especially the memory bandwidth - the lower the bandwidth is, the lower the ability to get to the maximum fill rate.