GeForce GT 640 DDR3 vs Radeon HD 4870 2GB

Intro

Compare those specs to the Radeon HD 4870 2GB, which has core speeds of 750 MHz on the GPU, and 900 MHz on the 2048 MB of GDDR5 memory. It features 800(160x5) SPUs along with 40 Texture Address Units and 16 Rasterization Operator Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
Radeon HD 4870 2GB		150 Watts
	Difference: 85 Watts (131%)

Memory Bandwidth

In theory, the Radeon HD 4870 2GB should be a lot faster than the GeForce GT 640 DDR3 overall. (explain)

Radeon HD 4870 2GB		115200 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 58176 (102%)

Texel Rate

The Radeon HD 4870 2GB will be a small bit (more or less 4%) better at AF than the GeForce GT 640 DDR3. (explain)

Radeon HD 4870 2GB		30000 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 1200 (4%)

Pixel Rate

If running with a high resolution is important to you, then the GeForce GT 640 DDR3 is superior to the Radeon HD 4870 2GB, though only just barely. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
Radeon HD 4870 2GB		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 largest amount of data (in units of MB per second) that can be moved over the external memory interface in a second. It is calculated by multiplying the bus width by its memory clock speed. If it uses DDR RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the bandwidth is, the better the card will be in general. It especially helps with AA, HDR and higher screen resolutions.

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

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