Compare any two graphics cards:
GeForce 8600 GT 256MB GDDR3 vs GeForce GT 320
IntroThe GeForce 8600 GT 256MB GDDR3 has a clock frequency of 540 MHz and a GDDR3 memory frequency of 700 MHz. It also features a 128-bit bus, and makes use of a 80 nm design. It is comprised of 32 SPUs, 16 Texture Address Units, and 8 Raster Operation Units.
Compare all that to the GeForce GT 320, which makes use of a 40 nm design. nVidia has clocked the core frequency at 540 MHz. The GDDR3 RAM runs at a frequency of 790 MHz on this specific card. It features 72 SPUs as well as 24 TAUs and 8 ROPs.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
Theoretically speaking, the GeForce GT 320 is 13% faster than the GeForce 8600 GT 256MB GDDR3 in general, because of its greater data rate. (explain)
Texel RateThe GeForce GT 320 should be a lot (more or less 50%) faster with regards to texture filtering than the GeForce 8600 GT 256MB GDDR3. (explain)
Pixel RateBoth cards have exactly the same pixel fill rate, so in theory they should perform equally good at at full screen anti-aliasing, and be able to handle the same screen resolutions. (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 data (in units of MB per second) that can be transferred across the external memory interface in one second. The number is worked out by multiplying the card's bus width by its memory speed. If the card has DDR memory, the result should be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The better the bandwidth is, the faster the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and higher screen resolutions.
Texel Rate: Texel rate is the maximum number of texture map elements (texels) that are applied in one second. This figure is worked out by multiplying the total number of texture units 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 per second.
Pixel Rate: Pixel rate is the most pixels that the graphics card can possibly record to the local memory in one second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the amount of Raster Operations Pipelines by the the card's clock speed. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel fill rate also depends on lots of other factors, especially the memory bandwidth - the lower the memory bandwidth is, the lower the ability to reach the maximum fill rate.