GeForce 9800 GT 512MB vs GeForce GT 640 DDR3

Intro

Compare all that to the GeForce GT 640 DDR3, which makes use of a 28 nm design. nVidia has clocked the core speed at 900 MHz. The DDR3 memory runs at a frequency of 1782 MHz on this specific model. It features 384 SPUs as well as 32 Texture Address Units and 16 Rasterization Operator Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce 9800 GT 512MB		105 Watts
	Difference: 40 Watts (62%)

Memory Bandwidth

In theory, the GeForce 9800 GT 512MB is 1% quicker than the GeForce GT 640 DDR3 overall, due to its greater bandwidth. (explain)

GeForce 9800 GT 512MB		57600 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 576 (1%)

Texel Rate

The GeForce 9800 GT 512MB will be a small bit (approximately 17%) better at anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce 9800 GT 512MB		33600 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 4800 (17%)

Pixel Rate

The GeForce GT 640 DDR3 will be much (approximately 50%) better at AA than the GeForce 9800 GT 512MB, and also should be able to handle higher resolutions while still performing well. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 9800 GT 512MB		9600 Mpixels/sec
	Difference: 4800 (50%)

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 data (measured in MB per second) that can be transported over the external memory interface in a second. It's worked out by multiplying the card's interface width by its memory speed. In the case of DDR memory, it should be multiplied by 2 once again. If it uses DDR5, multiply by ANOTHER 2x. The higher the memory bandwidth, the faster the card will be in general. It especially helps with anti-aliasing, HDR and higher screen resolutions.

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

Pixel Rate: Pixel rate is the maximum number of pixels the graphics card can possibly write to the local memory in a second - measured in millions of pixels per second. The figure is calculated by multiplying the amount of Raster Operations Pipelines by the the core speed of the card. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel 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 max fill rate.