GeForce GT 640 DDR3 vs GeForce GTX 460

Intro

Compare that to the GeForce GTX 460, which comes with a clock frequency of 675 MHz and a GDDR5 memory frequency of 900 MHz. It also features a 192-bit memory bus, and makes use of a 40 nm design. It features 336 SPUs, 56 Texture Address Units, and 24 Raster Operation Units.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3		65 Watts
GeForce GTX 460		150 Watts
	Difference: 85 Watts (131%)

Memory Bandwidth

As far as performance goes, the GeForce GTX 460 should theoretically be a lot superior to the GeForce GT 640 DDR3 overall. (explain)

GeForce GTX 460		86400 MB/sec
GeForce GT 640 DDR3		57024 MB/sec
	Difference: 29376 (52%)

Texel Rate

The GeForce GTX 460 should be a lot (more or less 31%) faster with regards to texture filtering than the GeForce GT 640 DDR3. (explain)

GeForce GTX 460		37800 Mtexels/sec
GeForce GT 640 DDR3		28800 Mtexels/sec
	Difference: 9000 (31%)

Pixel Rate

The GeForce GTX 460 will be just a bit (about 13%) more effective at AA than the GeForce GT 640 DDR3, and also should be able to handle higher resolutions without losing too much performance. (explain)

GeForce GTX 460		16200 Mpixels/sec
GeForce GT 640 DDR3		14400 Mpixels/sec
	Difference: 1800 (13%)

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 transported over the external memory interface within a second. The number is worked out by multiplying the card's interface width by the speed of its memory. If the card has DDR type memory, it must 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 amount of texture map elements (texels) that can be applied per second. This is worked out by multiplying the total amount of texture units by the core 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 in one second.

Pixel Rate: Pixel rate is the most pixels the video card could possibly record to the local memory per 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 filling the screen with pixels (the image). The actual pixel fill rate also depends on lots of other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to get to the maximum fill rate.