GeForce GT 640 DDR3 vs GeForce GTS 450 1GB

Intro

Compare those specifications to the GeForce GTS 450 1GB, which uses a 40 nm design. nVidia has clocked the core speed at 783 MHz. The GDDR5 memory works at a speed of 902 MHz on this card. It features 192 SPUs along with 32 TAUs and 16 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce GTS 450 1GB		106 Watts
	Difference: 41 Watts (63%)

Memory Bandwidth

Theoretically speaking, the GeForce GTS 450 1GB will be 1% quicker than the GeForce GT 640 DDR3 in general, due to its greater data rate. (explain)

GeForce GTS 450 1GB		57728 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 704 (1%)

Texel Rate

The GeForce GT 640 DDR3 is a small bit (approximately 15%) better at AF than the GeForce GTS 450 1GB. (explain)

GeForce GT 640 DDR3		28800 Mtexels/sec
GeForce GTS 450 1GB		25056 Mtexels/sec
	Difference: 3744 (15%)

Pixel Rate

If running with a high screen resolution is important to you, then the GeForce GT 640 DDR3 is a better choice, though not by far. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce GTS 450 1GB		12528 Mpixels/sec
	Difference: 1872 (15%)

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

Specifications

Memory Bandwidth: Bandwidth is the max amount of data (in units of MB per second) that can be transferred across the external memory interface in one second. It's worked out by multiplying the interface width by the speed of its memory. In the case of DDR RAM, it must be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the memory bandwidth, the better the card will be in general. It especially helps with anti-aliasing, HDR and high resolutions.

Texel Rate: Texel rate is the maximum texture map elements (texels) that are processed in one second. This number is calculated by multiplying the total number of texture units by the core clock speed of the chip. The better 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 that the graphics chip can possibly write to the local memory in one second - measured in millions of pixels per second. The number is worked out by multiplying the amount of colour ROPs by the the card's clock speed. ROPs (Raster Operations Pipelines - also called Render Output Units) are responsible for drawing the pixels (image) on the screen. The actual pixel fill rate is also dependant on lots of other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the ability to get to the max fill rate.