GeForce GT 640 DDR3 vs Radeon HD 4870 512MB

Intro

Compare those specifications to the Radeon HD 4870 512MB, which makes use of a 55 nm design. AMD has clocked the core speed at 750 MHz. The GDDR5 memory works at a speed of 900 MHz on this specific model. It features 800(160x5) SPUs along with 40 Texture Address Units and 16 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
Radeon HD 4870 512MB		150 Watts
	Difference: 85 Watts (131%)

Memory Bandwidth

In theory, the Radeon HD 4870 512MB should perform quite a bit faster than the GeForce GT 640 DDR3 in general. (explain)

Radeon HD 4870 512MB		115200 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 58176 (102%)

Texel Rate

The Radeon HD 4870 512MB should be just a bit (more or less 4%) more effective at AF than the GeForce GT 640 DDR3. (explain)

Radeon HD 4870 512MB		30000 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 1200 (4%)

Pixel Rate

The GeForce GT 640 DDR3 is a bit (approximately 20%) better at anti-aliasing than the Radeon HD 4870 512MB, and should be able to handle higher screen resolutions better. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
Radeon HD 4870 512MB		12000 Mpixels/sec
	Difference: 2400 (20%)

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 megabytes per second) that can be transferred across the external memory interface in one second. The number is calculated by multiplying the card's bus width by the speed of its memory. If the card has DDR memory, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The higher the bandwidth is, 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 number of texture map elements (texels) that are processed in one second. This figure is worked out by multiplying the total texture units 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 per second.

Pixel Rate: Pixel rate is the maximum number of pixels the video card can possibly record to the local memory in one second - measured in millions of pixels per second. The figure is worked out by multiplying the number of ROPs by the the core speed of the card. ROPs (Raster Operations Pipelines - also sometimes called Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel rate also depends on lots of other factors, especially the memory bandwidth - the lower the memory bandwidth is, the lower the potential to reach the maximum fill rate.