GeForce 820M vs GeForce GT 420

Intro

Compare that to the GeForce GT 420, which uses a 40 nm design. nVidia has clocked the core frequency at 700 MHz. The GDDR3 memory is set to run at a frequency of 900 MHz on this specific card. It features 48 SPUs as well as 8 TAUs and 4 ROPs.

Display Graphs

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Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce 820M		15 Watts
GeForce GT 420		50 Watts
	Difference: 35 Watts (233%)

Memory Bandwidth

The GeForce GT 420 should in theory be much faster than the GeForce 820M in general. (explain)

GeForce GT 420		28800 MB/sec
GeForce 820M		16000 MB/sec
	Difference: 12800 (80%)

Texel Rate

The GeForce 820M is much (about 105%) better at AF than the GeForce GT 420. (explain)

GeForce 820M		11504 Mtexels/sec
GeForce GT 420		5600 Mtexels/sec
	Difference: 5904 (105%)

Pixel Rate

If running with high levels of AA is important to you, then the GeForce 820M is superior to the GeForce GT 420, but not by far. (explain)

GeForce 820M		2876 Mpixels/sec
GeForce GT 420		2800 Mpixels/sec
	Difference: 76 (3%)

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 max amount of data (in units of MB per second) that can be moved across the external memory interface in a second. The number is worked out by multiplying the bus width by its memory speed. In the case of DDR type RAM, it must be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The higher 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 can be applied per second. This figure is worked out by multiplying the total number of texture units by the core clock 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 processed in one second.

Pixel Rate: Pixel rate is the maximum amount of pixels that the graphics chip could possibly write to its local memory in a second - measured in millions of pixels per second. Pixel rate is worked out by multiplying the amount of Render Output Units by the the core clock speed. ROPs (Raster Operations Pipelines - aka Render Output Units) are responsible for filling the screen with pixels (the image). The actual pixel rate is also dependant on many other factors, most notably the memory bandwidth of the card - the lower the bandwidth is, the lower the potential to get to the max fill rate.