Radeon HD 3870 X2 1GB vs Radeon HD 6850

Intro

Compare all of that to the Radeon HD 6850, which has a clock frequency of 775 MHz and a GDDR5 memory speed of 1000 MHz. It also uses a 256-bit memory bus, and uses a 40 nm design. It is comprised of 960 SPUs, 48 Texture Address Units, and 32 ROPs.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Memory Bandwidth

In theory, the Radeon HD 3870 X2 1GB should be 13% faster than the Radeon HD 6850 overall, due to its greater bandwidth. (explain)

Radeon HD 3870 X2 1GB		144128 MB/sec
Radeon HD 6850		128000 MB/sec
	Difference: 16128 (13%)

Texel Rate

The Radeon HD 6850 should be much (approximately 41%) more effective at AF than the Radeon HD 3870 X2 1GB. (explain)

Radeon HD 6850		37200 Mtexels/sec
Radeon HD 3870 X2 1GB		26400 Mtexels/sec
	Difference: 10800 (41%)

Pixel Rate

The Radeon HD 3870 X2 1GB is a small bit (more or less 6%) more effective at full screen anti-aliasing than the Radeon HD 6850, and also will be capable of handling higher resolutions better. (explain)

Radeon HD 3870 X2 1GB		26400 Mpixels/sec
Radeon HD 6850		24800 Mpixels/sec
	Difference: 1600 (6%)

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 (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 interface width by its memory clock speed. If it uses DDR type memory, it must be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The higher the card's memory bandwidth, the better the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and high resolutions.

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

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics chip can possibly write to the local memory per second - measured in millions of pixels per second. The figure is calculated by multiplying the amount of colour ROPs by the the card's 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 fill rate also depends on many other factors, especially the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to reach the maximum fill rate.