GeForce 9800 GX2 vs GeForce GT 640 DDR3

Intro

Compare that to the GeForce GT 640 DDR3, which features core speeds of 900 MHz on the GPU, and 1782 MHz on the 2048 MB of DDR3 memory. It features 384 SPUs as well as 32 Texture Address Units and 16 Rasterization Operator Units.

Display Graphs

Hide Graphs

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

The GeForce 9800 GX2, in theory, should perform much faster than the GeForce GT 640 DDR3 overall. (explain)

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

Texel Rate

The GeForce 9800 GX2 will be a lot (about 167%) more effective at anisotropic filtering 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

If running with lots of anti-aliasing is important to you, then the GeForce 9800 GX2 is the winner, by a large margin. (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 maximum amount of data (counted in MB per second) that can be moved past the external memory interface in a second. It is calculated by multiplying the interface width by the speed of its memory. If the card has DDR type RAM, it must be multiplied by 2 again. If DDR5, multiply by ANOTHER 2x. The better the memory bandwidth, the faster the card will be in general. It especially helps with AA, HDR and high resolutions.

Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that can be applied in one second. This is worked out by multiplying the total amount of texture units by the core clock speed of the chip. The better the texel rate, the better the video 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 amount of pixels that the graphics card could possibly record to the local memory in a second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the number of Render Output Units by the clock speed of the card. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel rate also depends on quite a few other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the maximum fill rate.