GeForce GT 640 DDR3 vs Radeon HD 4890 2GB

Intro

Compare those specs to the Radeon HD 4890 2GB, which uses a 55 nm design. AMD has clocked the core frequency at 1000 MHz. The GDDR5 memory runs at a frequency of 975 MHz on this particular card. It features 800(160x5) SPUs as well as 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 4890 2GB		190 Watts
	Difference: 125 Watts (192%)

Memory Bandwidth

As far as performance goes, the Radeon HD 4890 2GB should theoretically be quite a bit superior to the GeForce GT 640 DDR3 overall. (explain)

Radeon HD 4890 2GB		124800 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 67776 (119%)

Texel Rate

The Radeon HD 4890 2GB should be quite a bit (approximately 39%) faster with regards to texture filtering than the GeForce GT 640 DDR3. (explain)

Radeon HD 4890 2GB		40000 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 11200 (39%)

Pixel Rate

The Radeon HD 4890 2GB will be a bit (about 11%) faster with regards to FSAA than the GeForce GT 640 DDR3, and should be capable of handling higher resolutions without losing too much performance. (explain)

Radeon HD 4890 2GB		16000 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 1600 (11%)

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 (measured in megabytes per second) that can be transferred over the external memory interface in a second. The number is worked out by multiplying the card's bus width by its memory clock speed. If the card has DDR RAM, it should be multiplied by 2 once 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 anti-aliasing, High Dynamic Range and high resolutions.

Texel Rate: Texel rate is the maximum amount of texture map elements (texels) that can be processed in one second. This is calculated by multiplying the total texture units by the core clock speed of the chip. The higher the texel rate, the better the video card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels applied in one second.

Pixel Rate: Pixel rate is the most pixels that the graphics card can possibly record to the local memory in a second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the amount of Raster Operations Pipelines by the the core speed of the card. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel output rate also depends on quite a few other factors, especially the memory bandwidth - the lower the memory bandwidth is, the lower the ability to reach the max fill rate.