Compare any two graphics cards:
GeForce 8600 GT 1GB DDR2 vs Radeon HD 4550 512MB
IntroThe GeForce 8600 GT 1GB DDR2 comes with a clock speed of 540 MHz and a DDR2 memory frequency of 400 MHz. It also makes use of a 128-bit memory bus, and makes use of a 80 nm design. It is comprised of 32 SPUs, 16 TAUs, and 8 Raster Operation Units.
Compare all that to the Radeon HD 4550 512MB, which features clock speeds of 600 MHz on the GPU, and 800 MHz on the 512 MB of GDDR3 RAM. It features 80(16x5) SPUs as well as 8 Texture Address Units and 4 ROPs.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
Both cards have exactly the same memory bandwidth, so theoretically they should have the same performance. (explain)
Texel RateThe GeForce 8600 GT 1GB DDR2 is much (about 80%) better at texture filtering than the Radeon HD 4550 512MB. (explain)
Pixel RateIf using a high screen resolution is important to you, then the GeForce 8600 GT 1GB DDR2 is the winner, by a large margin. (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 maximum amount of information (measured in MB per second) that can be transported across the external memory interface in a second. It is calculated by multiplying the interface width by the speed of its memory. If the card has DDR RAM, it must be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The better the memory bandwidth, the better the card will be in general. It especially helps with AA, High Dynamic Range and higher screen resolutions.
Texel Rate: Texel rate is the maximum texture map elements (texels) that are processed in one second. This figure is calculated by multiplying the total amount of texture units of the card by the core clock speed of the chip. The higher this number, the better the graphics card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels in a second.
Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics card can possibly record to the local memory per second - measured in millions of pixels per second. The number is calculated by multiplying the amount of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel output rate is also dependant on quite a few other factors, especially the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the max fill rate.