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 features a 384-bit bus, and makes use of a 40 nm design. It is made up of 512 SPUs, 64 TAUs, and 48 Raster Operation Units.

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

As far as performance goes, the GeForce GTX 580 3GB should in theory be a lot better than the GeForce GT 640 DDR3 in general. (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 a lot (approximately 72%) better at texture 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

The GeForce GTX 580 3GB should be quite a bit (more or less 157%) more effective at anti-aliasing than the GeForce GT 640 DDR3, and also will be able to handle higher screen resolutions while still performing well. (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: Bandwidth is the max amount of information (in units of MB per second) that can be transported past the external memory interface in one second. It is worked out by multiplying the card's interface width by the speed of its memory. If the card has DDR type RAM, it should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the card's memory bandwidth, the faster the card will be in general. It especially helps with AA, High Dynamic Range and high resolutions.

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

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics chip could possibly record to the local memory in one second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the number of colour ROPs by the the core speed of the card. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate is also dependant on quite a few other factors, especially the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to reach the maximum fill rate.