GeForce 9800 GX2 vs GeForce GT 640 DDR3

Intro

Compare those specs to the GeForce GT 640 DDR3, which has a core clock frequency of 900 MHz and a DDR3 memory speed of 1782 MHz. It also makes use of a 128-bit memory bus, and makes use of a 28 nm design. It features 384 SPUs, 32 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 9800 GX2		197 Watts
	Difference: 132 Watts (203%)

Memory Bandwidth

As far as performance goes, the GeForce 9800 GX2 should theoretically be a lot superior to the GeForce GT 640 DDR3 in general. (explain)

GeForce 9800 GX2		128000 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 70976 (124%)

Texel Rate

The GeForce 9800 GX2 should be a lot (about 167%) faster with regards to AF than the GeForce GT 640 DDR3. (explain)

GeForce 9800 GX2		76800 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 48000 (167%)

Pixel Rate

The GeForce 9800 GX2 is much (more or less 33%) more effective at FSAA than the GeForce GT 640 DDR3, and will be capable of handling higher screen resolutions without slowing down too much. (explain)

GeForce 9800 GX2		19200 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 4800 (33%)

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.

One or more cards in this comparison are multi-core. This means that their bandwidth, texel and pixel rates are theoretically doubled - this does not mean the card will actually perform twice as fast, but only that it should in theory be able to. Actual game benchmarks will give a more accurate idea of what it's capable of.

Price Comparison

Specifications

Memory Bandwidth: Bandwidth is the largest amount of information (counted in MB per second) that can be transported past the external memory interface within a second. The number is worked out by multiplying the interface width by its memory clock speed. If it uses DDR type memory, the result should be multiplied by 2 again. If DDR5, multiply by 4 instead. The better the bandwidth is, the better the card will be in general. It especially helps with AA, High Dynamic Range and high resolutions.

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

Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics card could possibly record to the local memory per second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the amount 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 rate also depends on many other factors, especially the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to reach the maximum fill rate.