Radeon HD 3870 X2 512MB vs Radeon HD 4870 2GB

Intro

Compare those specifications to the Radeon HD 4870 2GB, which uses a 55 nm design. AMD has set the core speed at 750 MHz. The GDDR5 memory is set to run at a speed of 900 MHz on this model. It features 800(160x5) SPUs along with 40 TAUs and 16 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Memory Bandwidth

Both cards have exactly the same memory bandwidth, so theoretically they should perform exactly the same. (explain)

Texel Rate

The Radeon HD 4870 2GB is a small bit (more or less 14%) more effective at AF than the Radeon HD 3870 X2 512MB. (explain)

Radeon HD 4870 2GB		30000 Mtexels/sec
Radeon HD 3870 X2 512MB		26400 Mtexels/sec
	Difference: 3600 (14%)

Pixel Rate

The Radeon HD 3870 X2 512MB should be quite a bit (about 120%) more effective at full screen anti-aliasing than the Radeon HD 4870 2GB, and also will be capable of handling higher screen resolutions more effectively. (explain)

Radeon HD 3870 X2 512MB		26400 Mpixels/sec
Radeon HD 4870 2GB		12000 Mpixels/sec
	Difference: 14400 (120%)

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 maximum amount of information (measured in MB per second) that can be transported over the external memory interface in a second. It's calculated by multiplying the bus width by its memory speed. In the case of DDR type RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. 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 amount of texture map elements (texels) that are applied per second. This number is calculated by multiplying the total texture units of the card by the core clock speed of the chip. The higher the texel rate, the better the 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 amount of pixels the video card can possibly record to its local memory in a second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the number of Render Output Units by the clock speed of the card. ROPs (Raster Operations Pipelines - also 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, especially the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to reach the max fill rate.