NVIDIA GeForce 820M (128-bit) vs 840M

Since it has twice as many ROPs (Raster Operations Pipelines), the NVIDIA GeForce 820M (128-bit) card provides better pixel fill rate, even though its graphics frequency is lower. Having higher pixel fillrate allows the GPU to draw more pixels on screen and off screen, which is beneficial for some 3D effects in games, or when playing at higher display resolutions.

Although it has slower graphics clock rate, the GeForce 820M (128-bit) graphics card comes with twice as many Texture Mapping Units (TMUs), resulting in better texture fill rate. Better maximum texture fill rate allows the GPU to utilize more sophisticated 3D effects and/or apply more textures to each textured picture element, which improves visual appearance of games and generated images.

Single Precision performance shows how fast the graphics card is at executing applications, that process only single-precision floating point data. The performance is measured in billions of Floating Point Operations Per Second, or GFLOPS. Generally, the more CUDA cores or stream processors the GPU has, and the the faster they run at, the higher Single Precision performance will be. The GeForce 840M graphics card has a modest lead here. Higher single-precision performance number means the graphics card will perform better in general computing applications. Since CUDA cores or stream processors are also used as vertex and geometry shaders for 3D image generation, higher performance is also beneficial to games.

To speed up processing, the graphics cards store 3D scene data, textures and intermediate data, used for image generation, in on-board memory. The video memory usually has much higher bandwidth than system RAM, and more bandwidth allows the GPU to run at higher screen resolutions, use larger and more detailed textures, and apply more complex 3D effects and filters. The bandwidth is dependent on memory type, speed, and width of memory interface. In this case, higher memory bandwidth of the GeForce 840M graphics card is due to higher memory clock.