GeForce GT 640 DDR3 vs GeForce GTS 250 512MB

Intro

Compare that to the GeForce GTS 250 512MB, which makes use of a 65/55 nm design. nVidia has set the core speed at 738 MHz. The GDDR3 memory works at a speed of 1100 MHz on this specific model. It features 128 SPUs along with 64 TAUs 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 GTS 250 512MB		145 Watts
	Difference: 80 Watts (123%)

Memory Bandwidth

Theoretically, the GeForce GTS 250 512MB should perform a lot faster than the GeForce GT 640 DDR3 in general. (explain)

GeForce GTS 250 512MB		70400 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 13376 (23%)

Texel Rate

The GeForce GTS 250 512MB should be quite a bit (approximately 64%) better at anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTS 250 512MB		47232 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 18432 (64%)

Pixel Rate

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

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce GTS 250 512MB		11808 Mpixels/sec
	Difference: 2592 (22%)

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: Bandwidth is the maximum amount of information (counted in megabytes per second) that can be transported across the external memory interface within a second. It's worked out by multiplying the bus width by its memory speed. If it uses DDR type memory, it must be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the memory bandwidth, the better the card will be in general. It especially helps with anti-aliasing, HDR and higher screen resolutions.

Texel Rate: Texel rate is the maximum number of texture map elements (texels) that can be applied per second. This is worked out by multiplying the total texture units of the card 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 applied in a second.

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics card could possibly record to the local memory per second - measured in millions of pixels per second. The number is worked out by multiplying the amount of colour ROPs by the clock speed of the card. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate is also dependant on lots of other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to reach the maximum fill rate.