In terms of overall gaming performance, the graphical capabilities of the GT 640 and the GeForce GT 640 are equal.

The GeForce GT 640 has a 2 MHz higher core clock speed and the same number of Texture Mapping Units as the GT 640. This results in the GeForce GT 640 providing 0.099999999999998 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 GeForce GT 640 has a 2 MHz higher core clock speed than the GT 640, but both GPUs exhibit the same Pixel Fill Rate. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

Both the GeForce GT 640 Zotac Synergy 2GB Edition and the GeForce GT 640 were released at the same time, so are likely to be quite similar.

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

The GeForce GT 640 has 2.9 GB/sec greater memory bandwidth than the GT 640, which means that the memory performance of the GeForce GT 640 is marginally better than the GT 640.

Both the GeForce GT 640 Zotac Synergy 2GB Edition and the GeForce GT 640 have 384 Shader Processing Units. Having the same number of SPUs and using the same architecture means that the performance they offer can be compared by looking at the memory bandwidth, Texture and Pixel Rates. In this case, the GeForce GT 640 has 0.099999999999998 GTexel/s better Texture Fill Rate and 2.9 GB/sec greater memory bandwidth, but the has GPixel/s better Pixel Fill Rate. Although the GPUs are very similar in performance, the GeForce GT 640 takes the edge.

The GeForce GT 640 Zotac Synergy 2GB Edition requires 65 Watts to run and the GeForce GT 640 requires 65 Watts. We would recommend a PSU with at least 350 Watts for the GT 640 and a PSU with at least 350 Watts for the GeForce GT 640. The two GPUs require the same amount of wattage to run. As such, there is no need to worry about which will more significantly affect your yearly electricity bills.