GeForce GT 640 DDR3 vs GeForce GTX 275

Intro

Compare those specifications to the GeForce GTX 275, which comes with core clock speeds of 633 MHz on the GPU, and 1134 MHz on the 896 MB of GDDR3 memory. It features 240 SPUs as well as 80 Texture Address Units and 28 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 GTX 275		219 Watts
	Difference: 154 Watts (237%)

Memory Bandwidth

The GeForce GTX 275, in theory, should perform quite a bit faster than the GeForce GT 640 DDR3 overall. (explain)

GeForce GTX 275		127008 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 69984 (123%)

Texel Rate

The GeForce GTX 275 is quite a bit (more or less 76%) faster with regards to texture filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTX 275		50640 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 21840 (76%)

Pixel Rate

If using lots of anti-aliasing is important to you, then the GeForce GTX 275 is superior to the GeForce GT 640 DDR3, by a large margin. (explain)

GeForce GTX 275		17724 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 3324 (23%)

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 largest amount of data (measured in megabytes per second) that can be transported over the external memory interface in one second. It is calculated by multiplying the card's bus width by the speed of its memory. If it uses DDR memory, the result should be multiplied by 2 again. If DDR5, multiply by 4 instead. The higher the memory bandwidth, the faster the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and high 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 by the core clock speed of the chip. The higher the texel rate, the better the card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed in one second.

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics chip can possibly write to the local memory in a second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the amount of colour ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel rate is also dependant on many other factors, most notably the memory bandwidth - the lower the memory bandwidth is, the lower the ability to reach the max fill rate.