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GeForce 9800 GT 1GB vs GeForce GT 640 DDR3

Intro

The GeForce 9800 GT 1GB comes with a clock speed of 600 MHz and a GDDR3 memory frequency of 900 MHz. It also features a 256-bit memory bus, and makes use of a 65/55 nm design. It is comprised of 112 SPUs, 56 Texture Address Units, and 16 Raster Operation Units.

Compare that to the GeForce GT 640 DDR3, which comes with a clock speed of 900 MHz and a DDR3 memory frequency of 1782 MHz. It also makes use of a 128-bit memory bus, and uses a 28 nm design. It is comprised of 384 SPUs, 32 TAUs, and 16 ROPs.

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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

Theoretically, the GeForce 9800 GT 1GB should be a little bit faster than the GeForce GT 640 DDR3 in general. (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 just a bit (approximately 17%) better at anisotropic filtering 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

If using high levels of AA is important to you, then the GeForce GT 640 DDR3 is a better choice, and very much so. (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: Bandwidth is the maximum amount of data (measured in megabytes per second) that can be moved across the external memory interface in a second. It's calculated by multiplying the bus width by its memory speed. If it uses DDR type RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The higher the card's memory bandwidth, the better the card will be in general. It especially helps with AA, HDR and high resolutions.

Texel Rate: Texel rate is the maximum texture map elements (texels) that are applied in one second. This figure is worked out by multiplying the total texture units of the card by the core clock 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 applied per second.

Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics chip can possibly write to the local memory in one second - measured in millions of pixels per second. The figure is calculated by multiplying the amount of colour ROPs by the clock speed of the card. ROPs (Raster Operations Pipelines - sometimes also referred to as Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel fill rate is also dependant on quite a few other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to reach the maximum fill rate.

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