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GeForce GT 640 DDR3 vs Radeon HD 4850 2GB

Intro

The GeForce GT 640 DDR3 features a clock frequency of 900 MHz and a DDR3 memory frequency of 1782 MHz. It also features a 128-bit memory bus, and uses a 28 nm design. It features 384 SPUs, 32 Texture Address Units, and 16 ROPs.

Compare all of that to the Radeon HD 4850 2GB, which uses a 55 nm design. AMD has clocked the core frequency at 625 MHz. The GDDR4 memory works at a speed of 993 MHz on this card. It features 800(160x5) SPUs as well as 40 Texture Address Units and 16 ROPs.

(No game benchmarks for this combination yet.)

Power Usage and Theoretical Benchmarks

Power Consumption (Max TDP)

GeForce GT 640 DDR3 65 Watts
Radeon HD 4850 2GB 110 Watts
Difference: 45 Watts (69%)

Memory Bandwidth

In theory, the Radeon HD 4850 2GB will be 11% faster than the GeForce GT 640 DDR3 overall, because of its greater bandwidth. (explain)

Radeon HD 4850 2GB 63552 MB/sec
GeForce GT 640 DDR3 57024 MB/sec
Difference: 6528 (11%)

Texel Rate

The GeForce GT 640 DDR3 should be a small bit (about 15%) better at AF than the Radeon HD 4850 2GB. (explain)

GeForce GT 640 DDR3 28800 Mtexels/sec
Radeon HD 4850 2GB 25000 Mtexels/sec
Difference: 3800 (15%)

Pixel Rate

If using high levels of AA is important to you, then the GeForce GT 640 DDR3 is the winner, by a large margin. (explain)

GeForce GT 640 DDR3 14400 Mpixels/sec
Radeon HD 4850 2GB 10000 Mpixels/sec
Difference: 4400 (44%)

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

GeForce GT 640 DDR3

Amazon.com

Radeon HD 4850 2GB

Amazon.com

Please note that the price comparisons are based on search keywords - sometimes it might show cards with very similar names that are not exactly the same as the one chosen in the comparison. We do try to filter out the wrong results as best we can, though.

Specifications

Model GeForce GT 640 DDR3 Radeon HD 4850 2GB
Manufacturer nVidia AMD
Year June 2012 Jun 25, 2008
Code Name GK107 RV770 PRO
Fab Process 28 nm 55 nm
Bus PCIe 3.0 x16 PCIe 2.0 x16
Memory 2048 MB 2048 MB
Core Speed 900 MHz 625 MHz
Shader Speed 900 MHz (N/A) MHz
Memory Speed 1782 MHz (3564 MHz effective) 993 MHz (1986 MHz effective)
Unified Shaders 384 800(160x5)
Texture Mapping Units 32 40
Render Output Units 16 16
Bus Type DDR3 GDDR4
Bus Width 128-bit 256-bit
DirectX Version DirectX 11.0 DirectX 10.1
OpenGL Version OpenGL 4.2 OpenGL 3.0
Power (Max TDP) 65 watts 110 watts
Shader Model 5.0 4.1
Bandwidth 57024 MB/sec 63552 MB/sec
Texel Rate 28800 Mtexels/sec 25000 Mtexels/sec
Pixel Rate 14400 Mpixels/sec 10000 Mpixels/sec

Memory Bandwidth: Bandwidth is the max amount of data (counted in megabytes per second) that can be transported past the external memory interface in one second. It's calculated by multiplying the card's interface width by its memory speed. If the card has DDR memory, the result should be multiplied by 2 again. If it uses DDR5, multiply by 4 instead. The better the bandwidth is, the better the card will be in general. It especially helps with AA, High Dynamic Range and high resolutions.

Texel Rate: Texel rate is the maximum texture map elements (texels) that can be applied per second. This figure is worked out by multiplying the total texture units by the core clock speed of the chip. The better this number, the better the card will be at handling texture filtering (anisotropic filtering - AF). It is measured in millions of texels applied in a second.

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

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