GeForce GT 640 DDR3 vs GeForce GTX 275

Intro

Compare those specs to the GeForce GTX 275, which has a core clock frequency of 633 MHz and a GDDR3 memory frequency of 1134 MHz. It also uses a 448-bit memory bus, and uses a 55 nm design. It is made up of 240 SPUs, 80 TAUs, and 28 Raster Operation Units.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce GTX 275		219 Watts
	Difference: 154 Watts (237%)

Memory Bandwidth

In theory, the GeForce GTX 275 should be 123% faster than the GeForce GT 640 DDR3 in general, due to its greater data rate. (explain)

GeForce GTX 275		127008 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 69984 (123%)

Texel Rate

The GeForce GTX 275 is a lot (approximately 76%) faster with regards to anisotropic filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTX 275		50640 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 21840 (76%)

Pixel Rate

The GeForce GTX 275 will be much (about 23%) better at FSAA than the GeForce GT 640 DDR3, and will be able to handle higher resolutions better. (explain)

GeForce GTX 275		17724 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 3324 (23%)

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: Memory bandwidth is the maximum amount of data (measured in MB per second) that can be moved across the external memory interface in one second. It is worked out by multiplying the card's bus width by its memory clock speed. If the card has DDR RAM, it must be multiplied by 2 once again. If it uses DDR5, multiply by 4 instead. The better the memory bandwidth, 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 applied in one second. This number is calculated by multiplying the total texture units by the core speed of the chip. The higher the texel rate, the better the graphics 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 amount of pixels the video card could possibly record to its local memory per second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the amount of Raster Operations Pipelines by the clock speed of the card. 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 rate is also dependant on many other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to reach the max fill rate.