Compare any two graphics cards:
GeForce GT 640 DDR3 vs GeForce GTX 580 3GB
IntroThe GeForce GT 640 DDR3 comes with clock speeds of 900 MHz on the GPU, and 1782 MHz on the 2048 MB of DDR3 RAM. It features 384 SPUs as well as 32 Texture Address Units and 16 Rasterization Operator Units.
Compare those specifications to the GeForce GTX 580 3GB, which has a clock speed of 772 MHz and a GDDR5 memory speed of 1002 MHz. It also makes use of a 384-bit memory bus, and makes use of a 40 nm design. It is made up of 512 SPUs, 64 Texture Address Units, and 48 Raster Operation Units.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
In theory, the GeForce GTX 580 3GB should be a lot faster than the GeForce GT 640 DDR3 overall. (explain)
Texel RateThe GeForce GTX 580 3GB should be much (more or less 72%) more effective at anisotropic filtering than the GeForce GT 640 DDR3. (explain)
Pixel RateThe GeForce GTX 580 3GB will be much (more or less 157%) faster with regards to FSAA than the GeForce GT 640 DDR3, and also will be capable of handling higher screen resolutions without slowing down too much. (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.
Please note that the price comparisons are based on search keywords - sometimes it might show cards with very similar names that are not exactly the same as the one chosen in the comparison. We do try to filter out the wrong results as best we can, though.
Memory Bandwidth: Memory bandwidth is the maximum amount of information (in units of megabytes per second) that can be transferred across the external memory interface in a second. It's calculated by multiplying the card's interface width by the speed of its memory. In the case of DDR type RAM, the result should be multiplied by 2 once again. If DDR5, multiply by 4 instead. The higher the bandwidth is, 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 can be applied per second. This number is calculated by multiplying the total number of texture units of the card by the core speed of the chip. The higher this number, the better the card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels in one second.
Pixel Rate: Pixel rate is the most pixels that the graphics card can possibly record to the local memory per second - measured in millions of pixels per second. The number is worked out by multiplying the amount of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel rate also depends on quite a few other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the max fill rate.