Radeon HD 4870 2GB vs Radeon HD 7870

Intro

Compare all that to the Radeon HD 7870, which comes with a core clock frequency of 1000 MHz and a GDDR5 memory speed of 1200 MHz. It also makes use of a 256-bit memory bus, and makes use of a 28 nm design. It is comprised of 1280 SPUs, 80 Texture Address Units, and 32 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

Radeon HD 4870 2GB		150 Watts
Radeon HD 7870		175 Watts
	Difference: 25 Watts (17%)

Memory Bandwidth

Theoretically speaking, the Radeon HD 7870 will be 33% faster than the Radeon HD 4870 2GB overall, because of its greater data rate. (explain)

Radeon HD 7870		153600 MB/sec
Radeon HD 4870 2GB		115200 MB/sec
	Difference: 38400 (33%)

Texel Rate

The Radeon HD 7870 should be a lot (approximately 167%) better at anisotropic filtering than the Radeon HD 4870 2GB. (explain)

Radeon HD 7870		80000 Mtexels/sec
Radeon HD 4870 2GB		30000 Mtexels/sec
	Difference: 50000 (167%)

Pixel Rate

The Radeon HD 7870 will be a lot (about 167%) more effective at full screen anti-aliasing than the Radeon HD 4870 2GB, and will be able to handle higher screen resolutions without losing too much performance. (explain)

Radeon HD 7870		32000 Mpixels/sec
Radeon HD 4870 2GB		12000 Mpixels/sec
	Difference: 20000 (167%)

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

Texel Rate: Texel rate is the maximum texture map elements (texels) that are applied in one second. This is worked out by multiplying the total number of texture units of the card by the core clock speed of the chip. The better the texel rate, 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 record to the local memory in one second - measured in millions of pixels per second. The number is worked out by multiplying the amount of Render Output Units by the the core clock speed. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for outputting the pixels (image) to 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 reach the maximum fill rate.