GeForce 8400 GS 512MB vs GeForce GT 640 DDR3

Intro

Compare those specs to the GeForce GT 640 DDR3, which features a GPU core clock speed of 900 MHz, and 2048 MB of DDR3 RAM set to run at 1782 MHz through a 128-bit bus. It also features 384 SPUs, 32 TAUs, and 16 Raster Operation Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce 8400 GS 512MB		40 Watts
GeForce GT 640 DDR3		65 Watts
	Difference: 25 Watts (63%)

Memory Bandwidth

In theory, the GeForce GT 640 DDR3 is 791% quicker than the GeForce 8400 GS 512MB in general, because of its greater data rate. (explain)

GeForce GT 640 DDR3		57024 MB/sec
GeForce 8400 GS 512MB		6400 MB/sec
	Difference: 50624 (791%)

Texel Rate

The GeForce GT 640 DDR3 will be a lot (more or less 454%) better at texture filtering than the GeForce 8400 GS 512MB. (explain)

GeForce GT 640 DDR3		28800 Mtexels/sec
GeForce 8400 GS 512MB		5200 Mtexels/sec
	Difference: 23600 (454%)

Pixel Rate

If running with lots of anti-aliasing is important to you, then the GeForce GT 640 DDR3 is a better choice, and very much so. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 8400 GS 512MB		2600 Mpixels/sec
	Difference: 11800 (454%)

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 (measured in megabytes per second) that can be transferred past the external memory interface within a second. It's worked out by multiplying the interface width by its memory speed. If the card has DDR RAM, it must be multiplied by 2 once 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 figure is calculated by multiplying the total texture units of the card by the core speed of the chip. The better this number, the better the video card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed in one second.

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics card can possibly write to the local memory in a second - measured in millions of pixels per second. The number is calculated by multiplying the amount of ROPs by the the core clock speed. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel fill rate is also dependant on lots of other factors, most notably the memory bandwidth of the card - the lower the memory bandwidth is, the lower the ability to get to the maximum fill rate.