GeForce GT 640 DDR3 vs Radeon HD 4850 X2 1GB

Intro

Compare those specs to the Radeon HD 4850 X2 1GB, which has GPU clock speed of 625 MHz, and 1024 MB of GDDR3 RAM set to run at 993 MHz through a 256-bit bus. It also features 800(160x5) Stream Processors, 40 Texture Address Units, and 16 Raster Operation Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
Radeon HD 4850 X2 1GB		250 Watts
	Difference: 185 Watts (285%)

Memory Bandwidth

Theoretically speaking, the Radeon HD 4850 X2 1GB will be 123% faster than the GeForce GT 640 DDR3 overall, due to its higher bandwidth. (explain)

Radeon HD 4850 X2 1GB		127104 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 70080 (123%)

Texel Rate

The Radeon HD 4850 X2 1GB should be quite a bit (about 74%) better at anisotropic filtering than the GeForce GT 640 DDR3. (explain)

Radeon HD 4850 X2 1GB		50000 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 21200 (74%)

Pixel Rate

The Radeon HD 4850 X2 1GB should be much (about 39%) better at anti-aliasing than the GeForce GT 640 DDR3, and also capable of handling higher screen resolutions without slowing down too much. (explain)

Radeon HD 4850 X2 1GB		20000 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 5600 (39%)

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: Memory bandwidth is the max amount of information (counted in megabytes per second) that can be moved across the external memory interface in one second. It is worked out by multiplying the card's interface width by its memory clock speed. If the card has DDR memory, the result should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the memory bandwidth, the faster the card will be in general. It especially helps with AA, High Dynamic Range and higher screen resolutions.

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

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