GeForce GT 420 vs GeForce GT 640 DDR3

Intro

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

Display Graphs

Hide Graphs

Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 420		50 Watts
GeForce GT 640 DDR3		65 Watts
	Difference: 15 Watts (30%)

Memory Bandwidth

The GeForce GT 640 DDR3 should theoretically be a lot faster than the GeForce GT 420 in general. (explain)

GeForce GT 640 DDR3		57024 MB/sec
GeForce GT 420		28800 MB/sec
	Difference: 28224 (98%)

Texel Rate

The GeForce GT 640 DDR3 is quite a bit (more or less 414%) faster with regards to anisotropic filtering than the GeForce GT 420. (explain)

GeForce GT 640 DDR3		28800 Mtexels/sec
GeForce GT 420		5600 Mtexels/sec
	Difference: 23200 (414%)

Pixel Rate

If running with a high resolution is important to you, then the GeForce GT 640 DDR3 is superior to the GeForce GT 420, by a large margin. (explain)

GeForce GT 640 DDR3		14400 Mpixels/sec
GeForce GT 420		2800 Mpixels/sec
	Difference: 11600 (414%)

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 megabytes per second) that can be transported across the external memory interface in one second. The number is worked out by multiplying the bus width by its memory clock speed. If the card has DDR RAM, the result should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better 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 number of texture map elements (texels) that are applied in one second. This figure is calculated by multiplying the total amount of texture units of the card by the core clock speed of the chip. The better the texel rate, the better the card will be at texture filtering (anisotropic filtering - AF). It is measured in millions of texels in a second.

Pixel Rate: Pixel rate is the maximum amount of pixels the video card could possibly write to its local memory per second - measured in millions of pixels per second. Pixel rate is calculated by multiplying the number 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 output rate is also dependant on quite a few other factors, most notably the memory bandwidth - the lower the bandwidth is, the lower the ability to get to the maximum fill rate.