GeForce GT 640 DDR3 vs Radeon HD 3850 X2

Intro

Compare those specifications to the Radeon HD 3850 X2, which comes with a core clock speed of 668 MHz and a GDDR3 memory frequency of 828 MHz. It also makes use of a 256-bit memory bus, and uses a 55 nm design. It is comprised of 320(64x5) SPUs, 16 TAUs, and 16 Raster Operation Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Memory Bandwidth

In theory, the Radeon HD 3850 X2 should perform quite a bit faster than the GeForce GT 640 DDR3 overall. (explain)

Radeon HD 3850 X2		105984 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 48960 (86%)

Texel Rate

The GeForce GT 640 DDR3 will be much (more or less 35%) more effective at texture filtering than the Radeon HD 3850 X2. (explain)

GeForce GT 640 DDR3		28800 Mtexels/sec
Radeon HD 3850 X2		21376 Mtexels/sec
	Difference: 7424 (35%)

Pixel Rate

The Radeon HD 3850 X2 will be a lot (approximately 48%) faster with regards to anti-aliasing than the GeForce GT 640 DDR3, and also able to handle higher screen resolutions without losing too much performance. (explain)

Radeon HD 3850 X2		21376 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 6976 (48%)

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 data (in units of megabytes per second) that can be transported over the external memory interface in a second. It's calculated by multiplying the card's bus width by its memory speed. If the card has DDR type RAM, it must be multiplied by 2 once again. If DDR5, multiply by 4 instead. The higher the bandwidth is, the better the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and higher screen resolutions.

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

Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics chip can possibly write to the local memory in one second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the number of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate also depends on lots of other factors, especially the memory bandwidth - the lower the memory bandwidth is, the lower the ability to get to the max fill rate.