Compare any two graphics cards:
Radeon HD 4850 2GB vs Radeon HD 6750 1GB
IntroThe Radeon HD 4850 2GB has a GPU clock speed of 625 MHz, and the 2048 MB of GDDR4 RAM is set to run at 993 MHz through a 256-bit bus. It also is comprised of 800(160x5) SPUs, 40 Texture Address Units, and 16 ROPs.
Compare that to the Radeon HD 6750 1GB, which has a GPU core clock speed of 725 MHz, and 1024 MB of GDDR5 RAM running at 1000 MHz through a 128-bit bus. It also is comprised of 720 Stream Processors, 36 TAUs, and 16 Raster Operation Units.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
The Radeon HD 6750 1GB should theoretically perform just a bit faster than the Radeon HD 4850 2GB in general. (explain)
Texel RateThe Radeon HD 6750 1GB should be a little bit (approximately 4%) more effective at anisotropic filtering than the Radeon HD 4850 2GB. (explain)
Pixel RateIf running with lots of anti-aliasing is important to you, then the Radeon HD 6750 1GB is superior to the Radeon HD 4850 2GB, but not by far. (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: Memory bandwidth is the maximum amount of data (counted in MB per second) that can be transferred across the external memory interface in a second. It is worked out by multiplying the card's bus width by the speed of its memory. If it uses DDR RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The better the card's memory bandwidth, the better the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and high resolutions.
Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that are applied per second. This figure is worked out by multiplying the total number of texture units by the core clock speed of the chip. The higher the texel rate, the better the video 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 number of pixels the graphics card can possibly write to its local memory in a second - measured in millions of pixels per second. The number is calculated by multiplying the number of colour ROPs by the the core clock speed. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel output rate is also dependant on lots of other factors, especially the memory bandwidth - the lower the memory bandwidth is, the lower the ability to get to the maximum fill rate.