Radeon HD 4790 vs Radeon HD 6870

Intro

Compare all that to the Radeon HD 6870, which comes with clock speeds of 900 MHz on the GPU, and 1050 MHz on the 1024 MB of GDDR5 RAM. It features 1120 SPUs as well as 56 Texture Address Units and 32 Rasterization Operator Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Memory Bandwidth

As far as performance goes, the Radeon HD 6870 should in theory be a lot superior to the Radeon HD 4790 overall. (explain)

Radeon HD 6870		134400 MB/sec
Radeon HD 4790		102400 MB/sec
	Difference: 32000 (31%)

Texel Rate

The Radeon HD 6870 is a lot (approximately 163%) more effective at AF than the Radeon HD 4790. (explain)

Radeon HD 6870		50400 Mtexels/sec
Radeon HD 4790		19200 Mtexels/sec
	Difference: 31200 (163%)

Pixel Rate

If running with lots of anti-aliasing is important to you, then the Radeon HD 6870 is the winner, and very much so. (explain)

Radeon HD 6870		28800 Mpixels/sec
Radeon HD 4790		9600 Mpixels/sec
	Difference: 19200 (200%)

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.

Price Comparison

Specifications

Memory Bandwidth: Memory bandwidth is the maximum amount of information (in units of MB per second) that can be transferred over the external memory interface in one second. The number is worked out by multiplying the card's bus width by its memory clock speed. If it uses DDR RAM, it should be multiplied by 2 again. If DDR5, multiply by 4 instead. The higher the memory bandwidth, the faster 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 can be processed in one second. This is calculated by multiplying the total number of texture units of the card by the core speed of the chip. The better this number, the better the video card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels processed in one second.

Pixel Rate: Pixel rate is the maximum amount of pixels the video card can possibly write to the local memory in a second - measured in millions of pixels per second. The figure is calculated by multiplying the number of Render Output Units by the the card's clock speed. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel output rate is also dependant on quite a few other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the maximum fill rate.