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GeForce GT 640 DDR3 vs Radeon HD 4850 2GB

Intro

The GeForce GT 640 DDR3 features a clock speed of 900 MHz and a DDR3 memory speed of 1782 MHz. It also features a 128-bit memory bus, and uses a 28 nm design. It is made up of 384 SPUs, 32 Texture Address Units, and 16 ROPs.

Compare all that to the Radeon HD 4850 2GB, which comes with a GPU core clock speed of 625 MHz, and 2048 MB of GDDR4 RAM set to run at 993 MHz through a 256-bit bus. It also is comprised of 800(160x5) Stream Processors, 40 TAUs, and 16 ROPs.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3 65 Watts
Radeon HD 4850 2GB 110 Watts
Difference: 45 Watts (69%)

Memory Bandwidth

Performance-wise, the Radeon HD 4850 2GB should theoretically be a little bit superior to the GeForce GT 640 DDR3 overall. (explain)

Radeon HD 4850 2GB 63552 MB/sec
GeForce GT 640 DDR3 57024 MB/sec
Difference: 6528 (11%)

Texel Rate

The GeForce GT 640 DDR3 is just a bit (approximately 15%) better at AF than the Radeon HD 4850 2GB. (explain)

GeForce GT 640 DDR3 28800 Mtexels/sec
Radeon HD 4850 2GB 25000 Mtexels/sec
Difference: 3800 (15%)

Pixel Rate

If running with lots of anti-aliasing is important to you, then the GeForce GT 640 DDR3 is the winner, by a large margin. (explain)

GeForce GT 640 DDR3 14400 Mpixels/sec
Radeon HD 4850 2GB 10000 Mpixels/sec
Difference: 4400 (44%)

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

GeForce GT 640 DDR3

Amazon.com

Radeon HD 4850 2GB

Amazon.com

Please note that the price comparisons are based on search keywords - sometimes it might show cards with very similar names that are not exactly the same as the one chosen in the comparison. We do try to filter out the wrong results as best we can, though.

Specifications

Model GeForce GT 640 DDR3 Radeon HD 4850 2GB
Manufacturer nVidia AMD
Year June 2012 Jun 25, 2008
Code Name GK107 RV770 PRO
Fab Process 28 nm 55 nm
Bus PCIe 3.0 x16 PCIe 2.0 x16
Memory 2048 MB 2048 MB
Core Speed 900 MHz 625 MHz
Shader Speed 900 MHz (N/A) MHz
Memory Speed 1782 MHz (3564 MHz effective) 993 MHz (1986 MHz effective)
Unified Shaders 384 800(160x5)
Texture Mapping Units 32 40
Render Output Units 16 16
Bus Type DDR3 GDDR4
Bus Width 128-bit 256-bit
DirectX Version DirectX 11.0 DirectX 10.1
OpenGL Version OpenGL 4.2 OpenGL 3.0
Power (Max TDP) 65 watts 110 watts
Shader Model 5.0 4.1
Bandwidth 57024 MB/sec 63552 MB/sec
Texel Rate 28800 Mtexels/sec 25000 Mtexels/sec
Pixel Rate 14400 Mpixels/sec 10000 Mpixels/sec

Memory Bandwidth: Bandwidth is the max amount of data (counted in MB per second) that can be transported over the external memory interface in a second. It is worked out by multiplying the card's bus width by the speed of its memory. If it uses DDR type memory, the result should be multiplied by 2 again. If DDR5, multiply by 4 instead. The better the memory bandwidth, the faster the card will be in general. It especially helps with AA, HDR and higher screen resolutions.

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

Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics chip can possibly record to the local memory in a second - measured in millions of pixels per second. The figure is calculated by multiplying the number of colour ROPs by the clock speed of the card. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel output rate also depends on lots of other factors, especially the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to reach the max fill rate.

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