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GeForce 9800 GT 1GB vs GeForce GT 640 DDR3

Intro

The GeForce 9800 GT 1GB features clock speeds of 600 MHz on the GPU, and 900 MHz on the 1024 MB of GDDR3 RAM. It features 112 SPUs as well as 56 TAUs and 16 Rasterization Operator Units.

Compare all of that to the GeForce GT 640 DDR3, which has GPU clock speed of 900 MHz, and 2048 MB of DDR3 RAM set to run at 1782 MHz through a 128-bit bus. It also is comprised of 384 SPUs, 32 TAUs, and 16 Raster Operation Units.

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce 9800 GT 1GB		105 Watts
	Difference: 40 Watts (62%)

Memory Bandwidth

In theory, the GeForce 9800 GT 1GB will be 1% quicker than the GeForce GT 640 DDR3 overall, because of its greater data rate. (explain)

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

Texel Rate

The GeForce 9800 GT 1GB should be a small bit (more or less 17%) more effective at AF than the GeForce GT 640 DDR3. (explain)

GeForce 9800 GT 1GB		33600 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 4800 (17%)

Pixel Rate

The GeForce GT 640 DDR3 will be much (about 50%) faster with regards to AA than the GeForce 9800 GT 1GB, and able to handle higher resolutions while still performing well. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce 9800 GT 1GB		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 1GB

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GeForce GT 640 DDR3

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Specifications

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Model	GeForce 9800 GT 1GB	GeForce GT 640 DDR3
Manufacturer	nVidia	nVidia
Year	July 2008	June 2012
Code Name	G92a/b	GK107
Memory	1024 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: Memory bandwidth is the largest amount of information (counted in megabytes per second) that can be moved past the external memory interface in one second. It's worked out by multiplying the card's bus width by its memory speed. If it uses DDR memory, it must be multiplied by 2 once again. If DDR5, multiply by 4 instead. The higher the card's memory bandwidth, the faster the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and higher screen resolutions.

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

Pixel Rate: Pixel rate is the maximum number of pixels that the graphics chip can possibly record to the local memory in a second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the number of Render Output Units 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 output rate is also dependant on many other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to get to the max fill rate.

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