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GeForce GT 640 DDR3 vs Radeon HD 4850 2GB

Intro

The GeForce GT 640 DDR3 makes use of a 28 nm design. nVidia has clocked the core frequency at 900 MHz. The DDR3 memory works at a frequency of 1782 MHz on this card. It features 384 SPUs along with 32 Texture Address Units and 16 ROPs.

Compare all of that to the Radeon HD 4850 2GB, which has a clock frequency of 625 MHz and a GDDR4 memory frequency of 993 MHz. It also features a 256-bit bus, and makes use of a 55 nm design. It is comprised of 800(160x5) SPUs, 40 Texture Address Units, and 16 Raster Operation Units.

(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

Theoretically, the Radeon HD 4850 2GB should be a small bit faster than 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 will be a small bit (about 15%) faster with regards to 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

The GeForce GT 640 DDR3 should be quite a bit (about 44%) more effective at FSAA than the Radeon HD 4850 2GB, and also capable of handling higher screen resolutions more effectively. (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 (measured in MB per second) that can be moved across the external memory interface in one second. The number is calculated by multiplying the bus width by its memory speed. If it uses DDR RAM, it must be multiplied by 2 again. If DDR5, multiply by 4 instead. The better the card's memory bandwidth, 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 number of texture map elements (texels) that can be applied in one second. This is calculated by multiplying the total number of texture units by the core speed of the chip. The higher this number, the better the card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels in one second.

Pixel Rate: Pixel rate is the maximum number of pixels the video card could possibly record to its local memory per second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the amount of ROPs by the the core 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 fill rate also depends on lots of other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the max fill rate.

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