GeForce 8800 GTS (G80) 320MB vs GeForce GT 640 DDR3

Intro

Compare that to the GeForce GT 640 DDR3, which features GPU clock speed of 900 MHz, and 2048 MB of DDR3 RAM set to run at 1782 MHz through a 128-bit bus. It also is comprised of 384 Stream Processors, 32 Texture Address Units, and 16 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce 8800 GTS (G80) 320MB		143 Watts
	Difference: 78 Watts (120%)

Memory Bandwidth

In theory, the GeForce 8800 GTS (G80) 320MB is 11% quicker than the GeForce GT 640 DDR3 overall, because of its higher data rate. (explain)

GeForce 8800 GTS (G80) 320MB		63360 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 6336 (11%)

Texel Rate

The GeForce GT 640 DDR3 will be a little bit (approximately 17%) better at anisotropic filtering than the GeForce 8800 GTS (G80) 320MB. (explain)

GeForce GT 640 DDR3		28800 Mtexels/sec
GeForce 8800 GTS (G80) 320MB		24624 Mtexels/sec
	Difference: 4176 (17%)

Pixel Rate

If running with high levels of AA is important to you, then the GeForce GT 640 DDR3 is the winner, by a large margin. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 8800 GTS (G80) 320MB		10260 Mpixels/sec
	Difference: 4140 (40%)

Please note that the above 'benchmarks' are all just theoretical - the results were calculated based on the card's specifications, and real-world performance may (and probably will) vary at least a bit.

Price Comparison

Specifications

Memory Bandwidth: Memory bandwidth is the max amount of information (in units of MB per second) that can be moved past the external memory interface in one second. It is calculated by multiplying the interface width by its memory clock speed. If it uses DDR RAM, the result should be multiplied by 2 once again. If DDR5, multiply by 4 instead. The better the bandwidth is, the better the card will be in general. It especially helps with AA, HDR and higher screen resolutions.

Texel Rate: Texel rate is the maximum texture map elements (texels) that can be processed per second. This figure is worked out by multiplying the total number of texture units of the card by the core speed of the chip. The better this number, the better the video card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels applied per second.

Pixel Rate: Pixel rate is the maximum amount of pixels the video card could possibly record to its local memory in one second - measured in millions of pixels per second. The figure is worked out by multiplying the amount of ROPs by the the core clock speed. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate also depends on many other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to get to the maximum fill rate.