Radeon HD 4790 vs Radeon HD 4870 X2

Intro

Compare those specs to the Radeon HD 4870 X2, which has a clock speed of 750 MHz and a GDDR5 memory speed of 900 MHz. It also uses a 256-bit memory bus, and makes use of a 55 nm design. It features 800(160x5) SPUs, 40 TAUs, and 16 Raster Operation Units.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Memory Bandwidth

Theoretically speaking, the Radeon HD 4870 X2 should be 125% quicker than the Radeon HD 4790 overall, because of its greater bandwidth. (explain)

Radeon HD 4870 X2		230400 MB/sec
Radeon HD 4790		102400 MB/sec
	Difference: 128000 (125%)

Texel Rate

The Radeon HD 4870 X2 is much (more or less 213%) more effective at texture filtering than the Radeon HD 4790. (explain)

Radeon HD 4870 X2		60000 Mtexels/sec
Radeon HD 4790		19200 Mtexels/sec
	Difference: 40800 (213%)

Pixel Rate

The Radeon HD 4870 X2 is a lot (about 150%) better at full screen anti-aliasing than the Radeon HD 4790, and also should be able to handle higher screen resolutions without losing too much performance. (explain)

Radeon HD 4870 X2		24000 Mpixels/sec
Radeon HD 4790		9600 Mpixels/sec
	Difference: 14400 (150%)

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: Memory bandwidth is the maximum amount of data (in units of MB per second) that can be moved across the external memory interface in one second. The number is calculated by multiplying the card's interface width by its memory speed. In the case of DDR type RAM, the result should be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The higher the 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 texture map elements (texels) that can be processed in one second. This number is worked out by multiplying the total texture units of the card by the core clock speed of the chip. The better the texel rate, the better the graphics 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 most pixels the graphics card can possibly write to its local memory per second - measured in millions of pixels per second. The number is calculated by multiplying the number of Raster Operations Pipelines by the the card's clock speed. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel fill rate is also dependant on quite a few other factors, most notably the memory bandwidth - the lower the memory bandwidth is, the lower the ability to get to the max fill rate.