In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GT 640M are significantly better than the Nvidia GeForce GT 550M 2GB.

The GT 550M has a 115 MHz higher core clock speed than the GeForce GT 640M, but the GeForce GT 640M has 16 more Texture Mapping Units than the GT 550M. As a result, the GeForce GT 640M exhibits a 8.2 GTexel/s better Texture Fill Rate than the GT 550M. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.

The GT 550M has a 115 MHz higher core clock speed than the GeForce GT 640M, but the GeForce GT 640M has 12 more Render Output Units than the GT 550M. As a result, the GeForce GT 640M exhibits a 7 GPixel/s better Pixel Fill Rate than the GT 550M. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

The GeForce GT 640M was released over a year more recently than the GT 550M, and so the GeForce GT 640M is likely to have better driver support, meaning it will be more optimized for running the latest games when compared to the GT 550M.

The GeForce GT 550M 2GB and the GeForce GT 640M have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.

The memory bandwidth of the GeForce GT 550M 2GB and the GeForce GT 640M are the same, which means the GT 550M and the GeForce GT 640M have equal limitations when it comes to graphical data transfer.

The GeForce GT 550M 2GB has 96 Shader Processing Units and the GeForce GT 640M has 384. However, the actual shader performance of the GT 550M is 142 and the actual shader performance of the GeForce GT 640M is 240. The GeForce GT 640M having 98 better shader performance and an altogether better performance when taking into account other relevant data means that the GeForce GT 640M delivers a marginally smoother and more efficient experience when processing graphical data than the GT 550M.

The GeForce GT 640M transistor size technology is 12 nm (nanometers) smaller than the GT 550M. This means that the GeForce GT 640M is expected to run slightly cooler and achieve higher clock frequencies than the GT 550M.

The GeForce GT 550M 2GB requires 35 Watts to run and the GeForce GT 640M requires 32 Watts. The GT 550M requires 3 Watts more than the GeForce GT 640M to run. The difference is not significant enough for the GT 550M to have a noticeably larger impact on your yearly electricity bills than the GeForce GT 640M.