Radeon HD 4870 X2 vs Radeon HD 6990

Intro

Compare that to the Radeon HD 6990, which has a clock frequency of 830 MHz and a GDDR5 memory frequency of 1250 MHz. It also makes use of a 256-bit memory bus, and uses a 40 nm design. It is comprised of 1536 SPUs, 96 TAUs, and 32 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

Radeon HD 4870 X2		350 Watts
Radeon HD 6990		375 Watts
	Difference: 25 Watts (7%)

Memory Bandwidth

The Radeon HD 6990 should in theory perform quite a bit faster than the Radeon HD 4870 X2 in general. (explain)

Radeon HD 6990		320000 MB/sec
Radeon HD 4870 X2		230400 MB/sec
	Difference: 89600 (39%)

Texel Rate

The Radeon HD 6990 should be quite a bit (about 166%) better at anisotropic filtering than the Radeon HD 4870 X2. (explain)

Radeon HD 6990		159360 Mtexels/sec
Radeon HD 4870 X2		60000 Mtexels/sec
	Difference: 99360 (166%)

Pixel Rate

If running with a high screen resolution is important to you, then the Radeon HD 6990 is a better choice, and very much so. (explain)

Radeon HD 6990		53120 Mpixels/sec
Radeon HD 4870 X2		24000 Mpixels/sec
	Difference: 29120 (121%)

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: Bandwidth is the largest amount of information (measured in megabytes per second) that can be moved over the external memory interface within a second. The number is worked out by multiplying the bus width by its memory clock speed. In the case of DDR RAM, it must be multiplied by 2 once again. If it uses DDR5, multiply by ANOTHER 2x. The higher the card's memory bandwidth, the better the card will be in general. It especially helps with AA, HDR and high resolutions.

Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that are processed per second. This figure is worked out by multiplying the total number of texture units of the card by the core speed of the chip. The higher the texel rate, the better the card will be at 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 graphics card could possibly write to its local memory in one second - measured in millions of pixels per second. The figure is calculated by multiplying the number of ROPs by the the core speed of the card. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel rate is also dependant on quite a few other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to reach the max fill rate.