Radeon HD 4890 2GB vs Radeon HD 6870

Intro

Compare that to the Radeon HD 6870, which has a GPU core clock speed of 900 MHz, and 1024 MB of GDDR5 RAM running at 1050 MHz through a 256-bit bus. It also is made up of 1120 SPUs, 56 TAUs, and 32 Raster Operation Units.

Display Graphs

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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

Theoretically speaking, the Radeon HD 6870 should perform just a bit faster than the Radeon HD 4890 2GB overall. (explain)

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

Texel Rate

The Radeon HD 6870 is a lot (approximately 26%) better at texture 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 should be a lot (approximately 80%) more effective at anti-aliasing than the Radeon HD 4890 2GB, and also will be able to handle higher screen resolutions while still performing well. (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

Specifications

Memory Bandwidth: Bandwidth is the max amount of data (in units of megabytes per second) that can be transferred across the external memory interface within a second. It's worked out by multiplying the card's interface width by the speed of its memory. In the case of DDR RAM, it must 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 higher screen resolutions.

Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that are processed per second. This is worked out by multiplying the total amount of texture units 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 in a second.

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics chip can possibly record to the local memory in a second - measured in millions of pixels per second. The figure is calculated by multiplying the number of Raster Operations Pipelines by the the core clock speed. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel output rate is also dependant on lots of other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to get to the maximum fill rate.