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GeForce 9800 GT 512MB vs GeForce GT 640 DDR3

Intro

The GeForce 9800 GT 512MB has a clock frequency of 600 MHz and a GDDR3 memory speed of 900 MHz. It also makes use of a 256-bit bus, and makes use of a 65/55 nm design. It is made up of 112 SPUs, 56 Texture Address Units, and 16 ROPs.

Compare those specifications to the GeForce GT 640 DDR3, which has core clock speeds of 900 MHz on the GPU, and 1782 MHz on the 2048 MB of DDR3 RAM. It features 384 SPUs along with 32 TAUs and 16 Rasterization Operator Units.

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce 9800 GT 512MB		105 Watts
	Difference: 40 Watts (62%)

Memory Bandwidth

As far as performance goes, the GeForce 9800 GT 512MB should in theory be a bit better than the GeForce GT 640 DDR3 in general. (explain)

GeForce 9800 GT 512MB		57600 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 576 (1%)

Texel Rate

The GeForce 9800 GT 512MB should be a small bit (more or less 17%) better at AF than the GeForce GT 640 DDR3. (explain)

GeForce 9800 GT 512MB		33600 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 4800 (17%)

Pixel Rate

The GeForce GT 640 DDR3 will be much (approximately 50%) better at full screen anti-aliasing than the GeForce 9800 GT 512MB, and also should be able to handle higher resolutions better. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 9800 GT 512MB		9600 Mpixels/sec
	Difference: 4800 (50%)

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

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GeForce 9800 GT 512MB

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GeForce GT 640 DDR3

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Specifications

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Model	GeForce 9800 GT 512MB	GeForce GT 640 DDR3
Manufacturer	nVidia	nVidia
Year	July 2008	June 2012
Code Name	G92a/b	GK107
Memory	512 MB	2048 MB
Core Speed	600 MHz	900 MHz
Memory Speed	1800 MHz	3564 MHz
Power (Max TDP)	105 watts	65 watts
Bandwidth	57600 MB/sec	57024 MB/sec
Texel Rate	33600 Mtexels/sec	28800 Mtexels/sec
Pixel Rate	9600 Mpixels/sec	14400 Mpixels/sec
Unified Shaders	112	384
Texture Mapping Units	56	32
Render Output Units	16	16
Bus Type	GDDR3	DDR3
Bus Width	256-bit	128-bit
Fab Process	65/55 nm	28 nm
Transistors	754 million	1300 million
Bus	PCIe x16 2.0	PCIe 3.0 x16
DirectX Version	DirectX 10	DirectX 11.0
OpenGL Version	OpenGL 3.0	OpenGL 4.2

Memory Bandwidth: Bandwidth is the maximum amount of data (counted in megabytes per second) that can be moved over the external memory interface in a second. It's worked out by multiplying the interface width by its memory clock speed. In the case of DDR type RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The better the bandwidth is, 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 texture map elements (texels) that can be applied in one second. This figure is worked out by multiplying the total amount of texture units by the core speed of the chip. The better the texel rate, the better the video card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels per second.

Pixel Rate: Pixel rate is the maximum number of pixels the video card could possibly write to the local memory in a second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the number of ROPs by the the core clock speed. 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 fill rate also depends on quite a few other factors, most notably the memory bandwidth of the card - the lower the memory bandwidth is, the lower the ability to get to the maximum fill rate.

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