GeForce 9800 GTX vs GeForce GT 640 DDR3

Intro

Compare those specifications to the GeForce GT 640 DDR3, which makes use of a 28 nm design. nVidia has set the core speed at 900 MHz. The DDR3 memory is set to run at a speed of 1782 MHz on this card. It features 384 SPUs along with 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 GTX		140 Watts
	Difference: 75 Watts (115%)

Memory Bandwidth

In theory, the GeForce 9800 GTX will be 23% faster than the GeForce GT 640 DDR3 in general, due to its greater data rate. (explain)

GeForce 9800 GTX		70400 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 13376 (23%)

Texel Rate

The GeForce 9800 GTX should be much (about 50%) faster with regards to anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce 9800 GTX		43200 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 14400 (50%)

Pixel Rate

The GeForce GT 640 DDR3 is much (approximately 33%) faster with regards to anti-aliasing than the GeForce 9800 GTX, and able to handle higher screen resolutions without slowing down too much. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 9800 GTX		10800 Mpixels/sec
	Difference: 3600 (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.

Price Comparison

Specifications

Memory Bandwidth: Bandwidth is the maximum amount of data (in units of MB per second) that can be moved across the external memory interface in one second. The number is calculated by multiplying the card's interface width by its memory clock speed. If the card has DDR type memory, it should be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The higher the memory bandwidth, the faster the card will be in general. It especially helps with anti-aliasing, HDR and high resolutions.

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

Pixel Rate: Pixel rate is the most pixels the video card can possibly record to its local memory in a second - measured in millions of pixels per second. The figure is worked out by multiplying the number of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - also 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 of the card - the lower the bandwidth is, the lower the ability to reach the maximum fill rate.