GeForce 8800 GT 512MB vs GeForce GT 640 DDR3

Intro

Compare those specifications to the GeForce GT 640 DDR3, which uses a 28 nm design. nVidia has set the core frequency at 900 MHz. The DDR3 memory works at a speed of 1782 MHz on this card. It features 384 SPUs as well as 32 Texture Address Units and 16 Rasterization Operator Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce 8800 GT 512MB		105 Watts
	Difference: 40 Watts (62%)

Memory Bandwidth

In theory, the GeForce 8800 GT 512MB should be 1% quicker than the GeForce GT 640 DDR3 overall, because of its higher bandwidth. (explain)

GeForce 8800 GT 512MB		57600 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 576 (1%)

Texel Rate

The GeForce 8800 GT 512MB will be just a bit (about 17%) better at texture filtering than the GeForce GT 640 DDR3. (explain)

GeForce 8800 GT 512MB		33600 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 4800 (17%)

Pixel Rate

The GeForce GT 640 DDR3 should be much (approximately 50%) better at FSAA than the GeForce 8800 GT 512MB, and also will be able to handle higher resolutions more effectively. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 8800 GT 512MB		9600 Mpixels/sec
	Difference: 4800 (50%)

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 megabytes per second) that can be transferred across the external memory interface in a second. It's calculated by multiplying the card's interface width by its memory speed. If it uses DDR type memory, it must be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The higher the card's memory bandwidth, the faster the card will be in general. It especially helps with anti-aliasing, HDR and high resolutions.

Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that are processed in one second. This is calculated by multiplying the total texture units by the core clock speed of the chip. The higher the texel rate, the better the video card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed per second.

Pixel Rate: Pixel rate is the maximum amount of pixels the video card can possibly write to the local memory in one second - measured in millions of pixels per second. Pixel rate is calculated 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 fill rate also depends on quite a few other factors, especially the memory bandwidth of the card - the lower the memory bandwidth is, the lower the ability to get to the max fill rate.