GeForce GT 640 DDR3 vs GeForce GTX 580 3GB

Intro

Compare those specifications to the GeForce GTX 580 3GB, which has a core clock frequency of 772 MHz and a GDDR5 memory frequency of 1002 MHz. It also uses a 384-bit memory bus, and uses a 40 nm design. It is comprised of 512 SPUs, 64 TAUs, and 48 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce GTX 580 3GB		244 Watts
	Difference: 179 Watts (275%)

Memory Bandwidth

In theory, the GeForce GTX 580 3GB should be a lot faster than the GeForce GT 640 DDR3 overall. (explain)

GeForce GTX 580 3GB		192384 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 135360 (237%)

Texel Rate

The GeForce GTX 580 3GB will be much (approximately 72%) better at anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTX 580 3GB		49408 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 20608 (72%)

Pixel Rate

If running with lots of anti-aliasing is important to you, then the GeForce GTX 580 3GB is superior to the GeForce GT 640 DDR3, by far. (explain)

GeForce GTX 580 3GB		37056 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 22656 (157%)

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 information (in units of MB per second) that can be moved over the external memory interface in one second. It's worked out by multiplying the card's interface width by the speed of its memory. In the case of DDR memory, it should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The higher the card's memory bandwidth, the better 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 number is calculated by multiplying the total amount of texture units of the card by the core clock speed of the chip. The higher the texel rate, the better the graphics card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels applied in one second.

Pixel Rate: Pixel rate is the most pixels that the graphics card could possibly record to its local memory in one second - measured in millions of pixels per second. The number is calculated by multiplying the number of Render Output Units by the the card's 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, especially the memory bandwidth - the lower the bandwidth is, the lower the potential to get to the max fill rate.