Compare any two graphics cards:
Radeon HD 7870 XT vs Radeon R9 M390X
IntroThe Radeon HD 7870 XT features a core clock speed of 925 MHz and a GDDR5 memory speed of 1500 MHz. It also makes use of a 256-bit bus, and uses a 28 nm design. It features 1536 SPUs, 96 Texture Address Units, and 32 Raster Operation Units.
Compare that to the Radeon R9 M390X, which comes with a clock speed of 723 MHz and a GDDR5 memory speed of 1250 MHz. It also makes use of a 256-bit bus, and makes use of a 28 nm design. It is made up of 2048 SPUs, 128 TAUs, and 32 ROPs.
Power Usage and Theoretical Benchmarks
Power Consumption (Max TDP)
The Radeon HD 7870 XT, in theory, should perform just a bit faster than the Radeon R9 M390X overall. (explain)
Texel RateThe Radeon R9 M390X is a small bit (more or less 4%) faster with regards to anisotropic filtering than the Radeon HD 7870 XT. (explain)
Pixel RateIf running with a high screen resolution is important to you, then the Radeon HD 7870 XT 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 max amount of information (in units of MB per second) that can be moved over the external memory interface in a second. The number is calculated by multiplying the card's bus width by its memory speed. If it uses DDR RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The higher the memory bandwidth, the better 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 texture map elements (texels) that are processed per second. This is worked out by multiplying the total texture units by the core speed of the chip. The higher this number, the better the graphics card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed per second.
Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics card could possibly write to its 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 core speed of the card. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate is also dependant on quite a few other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to get to the max fill rate.