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GeForce GT 640 DDR3 vs Radeon HD 7990

Intro

The GeForce GT 640 DDR3 comes with a GPU clock speed of 900 MHz, and the 2048 MB of DDR3 memory runs at 1782 MHz through a 128-bit bus. It also is made up of 384 SPUs, 32 TAUs, and 16 Raster Operation Units.

Compare those specifications to the Radeon HD 7990, which uses a 28 nm design. AMD has set the core speed at 950 MHz. The GDDR5 memory works at a frequency of 1500 MHz on this specific model. It features 2048 SPUs along with 128 TAUs and 32 ROPs.

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3 65 Watts
Radeon HD 7990 375 Watts
Difference: 310 Watts (477%)

Memory Bandwidth

The Radeon HD 7990 should theoretically be a lot faster than the GeForce GT 640 DDR3 overall. (explain)

Radeon HD 7990 576000 MB/sec
GeForce GT 640 DDR3 57024 MB/sec
Difference: 518976 (910%)

Texel Rate

The Radeon HD 7990 is much (about 744%) faster with regards to texture filtering than the GeForce GT 640 DDR3. (explain)

Radeon HD 7990 243200 Mtexels/sec
GeForce GT 640 DDR3 28800 Mtexels/sec
Difference: 214400 (744%)

Pixel Rate

The Radeon HD 7990 will be a lot (about 322%) more effective at anti-aliasing than the GeForce GT 640 DDR3, and also should be able to handle higher resolutions better. (explain)

Radeon HD 7990 60800 Mpixels/sec
GeForce GT 640 DDR3 14400 Mpixels/sec
Difference: 46400 (322%)

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.

One or more cards in this comparison are multi-core. This means that their bandwidth, texel and pixel rates are theoretically doubled - this does not mean the card will actually perform twice as fast, but only that it should in theory be able to. Actual game benchmarks will give a more accurate idea of what it's capable of.

Price Comparison

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GeForce GT 640 DDR3

Amazon.com

Radeon HD 7990

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

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Model GeForce GT 640 DDR3 Radeon HD 7990
Manufacturer nVidia AMD
Year June 2012 April 2013
Code Name GK107 Malta
Memory 2048 MB 3072 MB (x2)
Core Speed 900 MHz 950 MHz (x2)
Memory Speed 3564 MHz 6000 MHz (x2)
Power (Max TDP) 65 watts 375 watts
Bandwidth 57024 MB/sec 576000 MB/sec
Texel Rate 28800 Mtexels/sec 243200 Mtexels/sec
Pixel Rate 14400 Mpixels/sec 60800 Mpixels/sec
Unified Shaders 384 2048 (x2)
Texture Mapping Units 32 128 (x2)
Render Output Units 16 32 (x2)
Bus Type DDR3 GDDR5
Bus Width 128-bit 384-bit (x2)
Fab Process 28 nm 28 nm
Transistors 1300 million 4313 million
Bus PCIe 3.0 x16 PCIe 3.0 x16
DirectX Version DirectX 11.0 DirectX 11.1
OpenGL Version OpenGL 4.2 OpenGL 4.3

Memory Bandwidth: Memory bandwidth is the largest amount of data (counted in MB per second) that can be transported across the external memory interface in a second. It's calculated by multiplying the card's interface width by the speed of its memory. If it uses DDR type RAM, it must be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the card's memory bandwidth, the faster the card will be in general. It especially helps with AA, High Dynamic Range and high resolutions.

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

Pixel Rate: Pixel rate is the maximum number of pixels the video card could possibly write to the local memory in one second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the number of colour ROPs by the the core clock speed. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel fill rate also depends on quite a few other factors, especially the memory bandwidth of the card - the lower the memory bandwidth is, the lower the potential to reach the max fill rate.

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