In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce 9800 GT Green Edition are marginally better than the Nvidia GeForce GT 640.

The GeForce GT 640 has a 352 MHz higher core clock speed than the 9800 GT, but the 9800 GT has 24 more Texture Mapping Units than the GeForce GT 640. As a result, the 9800 GT exhibits a 1.9 GTexel/s better Texture Fill Rate than the GeForce GT 640. 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 352 MHz higher core clock speed than the 9800 GT and the same number of Render Output Units. This results in the GeForce GT 640 providing 5.6 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 GeForce GT 640 was released over three years more recently than the 9800 GT, and so the GeForce GT 640 is likely to have far better driver support, meaning it will be much more optimized and ultimately superior to the 9800 GT when running the latest games.

The GeForce GT 640 has 1536 MB more video memory than the 9800 GT, so is likely to be much better at displaying game textures at higher resolutions. However, overall, the 9800 GT has superior memory performance.

The 9800 GT has 29.1 GB/sec greater memory bandwidth than the GeForce GT 640, which means that the memory performance of the 9800 GT is slightly better than the GeForce GT 640.

The GeForce GT 640 has 384 Shader Processing Units and the GeForce 9800 GT Green Edition has 112. However, the actual shader performance of the GeForce GT 640 is 346 and the actual shader performance of the 9800 GT is 154. The GeForce GT 640 having 192 better shader performance is not particularly notable, as altogether the 9800 GT performs better when taking into account other relevant data.

The GeForce GT 640 transistor size technology is 37 nm (nanometers) smaller than the 9800 GT. This means that the GeForce GT 640 is expected to run much cooler and achieve higher clock frequencies than the 9800 GT. While they exhibit similar graphical performance, the GeForce GT 640 should consume less power than the 9800 GT.

The GeForce GT 640 requires 65 Watts to run and the GeForce 9800 GT Green Edition requires 75 Watts. We would recommend a PSU with at least 350 Watts for the GeForce GT 640 and a PSU with at least 400 Watts for the 9800 GT. The 9800 GT requires 10 Watts more than the GeForce GT 640 to run. The difference is not significant enough for the 9800 GT to have a noticeably larger impact on your yearly electricity bills than the GeForce GT 640.