In terms of overall gaming performance, the graphical capabilities of the AMD Radeon HD 7850 XFX Ultra OC Edition are massively better than the Nvidia GeForce GT 640 Zotac Zone 2GB Edition.

The HD 7850 has a 75 MHz higher core clock speed and 32 more Texture Mapping Units than the GT 640. This results in the HD 7850 providing 33.6 GTexel/s better texturing performance. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.

The HD 7850 has a 75 MHz higher core clock speed and 16 more Render Output Units than the GT 640. This results in the HD 7850 providing 16.8 GPixel/s better pixeling performance. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

The GT 640 was released less than a year after the HD 7850, and so they are likely to have similar driver support for optimizing performance when running the latest games.

The GT 640 has 1024 MB more video memory than the HD 7850, so is likely to be much better at displaying game textures at higher resolutions. However, overall, the HD 7850 has superior memory performance.

The HD 7850 has 125.1 GB/sec greater memory bandwidth than the GT 640, which means that the memory performance of the HD 7850 is massively better than the GT 640.

The GeForce GT 640 Zotac Zone 2GB Edition has 384 Shader Processing Units and the Radeon HD 7850 XFX Ultra OC Edition has 1024. However, the actual shader performance of the GT 640 is 346 and the actual shader performance of the HD 7850 is 849. The HD 7850 having 503 better shader performance and an altogether better performance when taking into account other relevant data means that the HD 7850 delivers a massively smoother and more efficient experience when processing graphical data than the GT 640.

The GeForce GT 640 Zotac Zone 2GB Edition requires 65 Watts to run but there is no entry for the Radeon HD 7850 XFX Ultra OC Edition. We would recommend a PSU with at least 350 Watts for the GT 640 and a PSU with at least 500 Watts for the HD 7850. The HD 7850 has been recommended a PSU with 150 Watts more than the GT 640. The difference is significant enough that the HD 7850 may have an adverse affect on your yearly electricity bills in comparison to the GT 640.