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Radeon HD 4890 2GB vs Radeon HD 6870

Intro

The Radeon HD 4890 2GB comes with core clock speeds of 1000 MHz on the GPU, and 975 MHz on the 2048 MB of GDDR5 memory. It features 800(160x5) SPUs as well as 40 Texture Address Units and 16 ROPs.

Compare that to the Radeon HD 6870, which makes use of a 40 nm design. AMD has set the core frequency at 900 MHz. The GDDR5 memory is set to run at a frequency of 1050 MHz on this model. It features 1120 SPUs along with 56 Texture Address Units and 32 Rasterization Operator Units.

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

Radeon HD 6870		151 Watts
Radeon HD 4890 2GB		190 Watts
	Difference: 39 Watts (26%)

Memory Bandwidth

The Radeon HD 6870, in theory, should perform a little bit faster than the Radeon HD 4890 2GB in general. (explain)

Radeon HD 6870		134400 MB/sec
Radeon HD 4890 2GB		124800 MB/sec
	Difference: 9600 (8%)

Texel Rate

The Radeon HD 6870 should be a lot (about 26%) more effective at anisotropic filtering than the Radeon HD 4890 2GB. (explain)

Radeon HD 6870		50400 Mtexels/sec
Radeon HD 4890 2GB		40000 Mtexels/sec
	Difference: 10400 (26%)

Pixel Rate

The Radeon HD 6870 is much (approximately 80%) more effective at full screen anti-aliasing than the Radeon HD 4890 2GB, and should be able to handle higher resolutions more effectively. (explain)

Radeon HD 6870		28800 Mpixels/sec
Radeon HD 4890 2GB		16000 Mpixels/sec
	Difference: 12800 (80%)

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

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Radeon HD 4890 2GB

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Radeon HD 6870

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Specifications

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Model	Radeon HD 4890 2GB	Radeon HD 6870
Manufacturer	AMD	AMD
Year	Apr 2, 2009	October 2010
Code Name	RV790 XT	Barts XT
Memory	2048 MB	1024 MB
Core Speed	1000 MHz	900 MHz
Memory Speed	3900 MHz	4200 MHz
Power (Max TDP)	190 watts	151 watts
Bandwidth	124800 MB/sec	134400 MB/sec
Texel Rate	40000 Mtexels/sec	50400 Mtexels/sec
Pixel Rate	16000 Mpixels/sec	28800 Mpixels/sec
Unified Shaders	800(160x5)	1120
Texture Mapping Units	40	56
Render Output Units	16	32
Bus Type	GDDR5	GDDR5
Bus Width	256-bit	256-bit
Fab Process	55 nm	40 nm
Transistors	959 million	1700 million
Bus	PCIe 2.0 x16	PCIe x16
DirectX Version	DirectX 10.1	DirectX 11
OpenGL Version	OpenGL 3.0	OpenGL 4.1

Memory Bandwidth: Memory bandwidth is the max amount of data (counted in megabytes per second) that can be transported across the external memory interface in a second. The number is calculated by multiplying the card's interface width by its memory speed. If it uses DDR RAM, it must be multiplied by 2 again. If DDR5, multiply by ANOTHER 2x. The higher the memory bandwidth, the better the card will be in general. It especially helps with anti-aliasing, HDR and high resolutions.

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

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

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