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GeForce 9800 GT 1GB vs GeForce GT 640 DDR3

Intro

The GeForce 9800 GT 1GB has a GPU core speed of 600 MHz, and the 1024 MB of GDDR3 memory is set to run at 900 MHz through a 256-bit bus. It also is comprised of 112 Stream Processors, 56 TAUs, and 16 ROPs.

Compare those specs to the GeForce GT 640 DDR3, which comes with core clock speeds of 900 MHz on the GPU, and 1782 MHz on the 2048 MB of DDR3 memory. It features 384 SPUs as well as 32 Texture Address Units 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 1GB		105 Watts
	Difference: 40 Watts (62%)

Memory Bandwidth

Theoretically, the GeForce 9800 GT 1GB should perform a bit faster than the GeForce GT 640 DDR3 overall. (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 is a bit (approximately 17%) better at texture 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

The GeForce GT 640 DDR3 is much (about 50%) better at full screen anti-aliasing than the GeForce 9800 GT 1GB, and should be able to handle higher resolutions better. (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 data (measured in MB per second) that can be transferred past the external memory interface in a second. The number is worked out by multiplying the bus width by its memory speed. If it uses DDR memory, it should be multiplied by 2 again. If it uses DDR5, multiply by ANOTHER 2x. The higher the bandwidth is, the faster the card will be in general. It especially helps with anti-aliasing, High Dynamic Range and high resolutions.

Texel Rate: Texel rate is the maximum number of texture map elements (texels) that are processed in one second. This figure is calculated by multiplying the total amount of texture units of the card 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 per second.

Pixel Rate: Pixel rate is the most pixels the video card can possibly record to its local memory in one second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the amount of colour ROPs by the the core speed of the card. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for outputting the pixels (image) to the screen. The actual pixel rate is also dependant on lots of 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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