GeForce GT 640 DDR3 vs Radeon HD 4890 1GB

Intro

Compare that to the Radeon HD 4890 1GB, which features core speeds of 1000 MHz on the GPU, and 975 MHz on the 1024 MB of GDDR5 RAM. It features 800(160x5) SPUs along with 40 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
Radeon HD 4890 1GB		190 Watts
	Difference: 125 Watts (192%)

Memory Bandwidth

In theory, the Radeon HD 4890 1GB will be 119% faster than the GeForce GT 640 DDR3 overall, because of its greater bandwidth. (explain)

Radeon HD 4890 1GB		124800 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 67776 (119%)

Texel Rate

The Radeon HD 4890 1GB is much (more or less 39%) more effective at texture filtering than the GeForce GT 640 DDR3. (explain)

Radeon HD 4890 1GB		40000 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 11200 (39%)

Pixel Rate

The Radeon HD 4890 1GB is a little bit (about 11%) faster with regards to AA than the GeForce GT 640 DDR3, and should be able to handle higher resolutions without slowing down too much. (explain)

Radeon HD 4890 1GB		16000 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 1600 (11%)

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 (counted in megabytes per second) that can be moved over the external memory interface in one second. The number is worked out by multiplying the card's interface width by the speed of its memory. In the case of DDR memory, it should be multiplied by 2 again. If DDR5, multiply by ANOTHER 2x. The better the memory bandwidth, the better 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 processed per second. This number is calculated by multiplying the total number of texture units by the core clock speed of the chip. The better this number, the better the graphics card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels applied in one second.

Pixel Rate: Pixel rate is the most pixels that the graphics chip could possibly record to its local memory per second - measured in millions of pixels per second. The number is worked out by multiplying the number of ROPs by the the core clock speed. ROPs (Raster Operations Pipelines - also sometimes called 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 - the lower the memory bandwidth is, the lower the potential to get to the maximum fill rate.