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GeForce GT 640 DDR3 vs GeForce GTX 660 Ti

Intro

The GeForce GT 640 DDR3 features a clock frequency of 900 MHz and a DDR3 memory frequency of 1782 MHz. It also features a 128-bit memory bus, and uses a 28 nm design. It features 384 SPUs, 32 TAUs, and 16 ROPs.

Compare those specs to the GeForce GTX 660 Ti, which has clock speeds of 915 MHz on the GPU, and 1500 MHz on the 2048 MB of GDDR5 RAM. It features 1344 SPUs along with 112 Texture Address Units and 24 Rasterization Operator Units.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3 65 Watts
GeForce GTX 660 Ti 150 Watts
Difference: 85 Watts (131%)

Memory Bandwidth

The GeForce GTX 660 Ti should in theory perform quite a bit faster than the GeForce GT 640 DDR3 overall. (explain)

GeForce GTX 660 Ti 144000 MB/sec
GeForce GT 640 DDR3 57024 MB/sec
Difference: 86976 (153%)

Texel Rate

The GeForce GTX 660 Ti will be quite a bit (approximately 256%) faster with regards to anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTX 660 Ti 102480 Mtexels/sec
GeForce GT 640 DDR3 28800 Mtexels/sec
Difference: 73680 (256%)

Pixel Rate

If using high levels of AA is important to you, then the GeForce GTX 660 Ti is the winner, and very much so. (explain)

GeForce GTX 660 Ti 21960 Mpixels/sec
GeForce GT 640 DDR3 14400 Mpixels/sec
Difference: 7560 (53%)

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

GeForce GTX 660 Ti

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 GeForce GTX 660 Ti
Manufacturer nVidia nVidia
Year June 2012 August 2012
Code Name GK107 GK104
Fab Process 28 nm 28 nm
Bus PCIe 3.0 x16 PCIe 3.0 x16
Memory 2048 MB 2048 MB
Core Speed 900 MHz 915 MHz
Shader Speed 900 MHz 915 MHz
Memory Speed 1782 MHz (3564 MHz effective) 1500 MHz (6000 MHz effective)
Unified Shaders 384 1344
Texture Mapping Units 32 112
Render Output Units 16 24
Bus Type DDR3 GDDR5
Bus Width 128-bit 192-bit
DirectX Version DirectX 11.0 DirectX 11.0
OpenGL Version OpenGL 4.2 OpenGL 4.3
Power (Max TDP) 65 watts 150 watts
Shader Model 5.0 5.0
Bandwidth 57024 MB/sec 144000 MB/sec
Texel Rate 28800 Mtexels/sec 102480 Mtexels/sec
Pixel Rate 14400 Mpixels/sec 21960 Mpixels/sec

Memory Bandwidth: Memory bandwidth is the largest amount of information (in units of MB per second) that can be moved across the external memory interface within a second. It's worked out by multiplying the bus width by its memory clock speed. If the card has DDR type memory, it must be multiplied by 2 again. If DDR5, multiply by 4 instead. The higher the memory bandwidth, the better the card will be in general. It especially helps with AA, High Dynamic Range and high resolutions.

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

Pixel Rate: Pixel rate is the most pixels the video card can possibly write to the local memory in one second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the amount of ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel rate also depends on many other factors, most notably the memory bandwidth of the card - the lower the memory bandwidth is, the lower the ability to get to the max fill rate.

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