NVIDIA GeForce GTX 670MX SLI vs NVIDIA GeForce GTX 680M

NVIDIA GeForce GTX 670MX SLI

The NVIDIA GeForce GTX 670MX SLI is a high-end DirectX 11-compatible graphics card for laptops, consisting of two GeForce GTX 670MX. Each card has a 28nm GK104 core based on the Kepler architecture. With SLI, each card usually renders a single frame (AFR mode). Therefore, it may suffer from micro stuttering in low fps ranges of 30fps. This happens because of different timespans between two frames (e.g., irregular delays between sequential frames).

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK106 Kepler core offers five shader blocks, called SMX, that are clocked at the same speed as the central core. In the GTX 670MX, all 5 blocks are active leading to the 960 CUDA cores. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are of similar speed to one shader of a Fermi chip (as the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

The graphics performance of the GeForce GTX 670MX SLI depends on the driver support of the benchmark / game. Ideally it can be up to twice as fast as a single GTX 670MX, ranking it as one of the fastest mobile graphics solution for laptops in 2012. The performance should be on average similar to a single GTX 680M, but with the problems of micro stuttering (see above) and a higher power consumption. The GPUs have enough power to run games of 2012 fluently with Full HD resolution, maxed out graphical settings and antialiasing. Even extremely demanding titles like Metro 2033, Alan Wake or Risen 2 are playable at the highest detail settings.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK104 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENC API.

Power Consumption

The power consumption of the GeForce GTX 670MX SLI should double compared to a single GTX 670MX. Therefore, only large desktop replacements can handle the heat.

NVIDIA GeForce GTX 680M

The NVIDIA GeForce GTX 680M is a high-end DirectX 11.1-compatible graphics card for laptops and was announced during Computex 2012. It was the fastest GPU available for notebooks at the time of announcement and has a 28nm GK104 core based on the Kepler architecture. Compared to the desktop GeForce GTX 670, the GTX 680M also features 1344 CUDA cores, but the mobile counterpart operates at reduced core and memory clock speeds (720/1800MHz vs 915-980/3004MHz).

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK104 Kepler core offers eight shader blocks, called SMX, that are clocked at the same speed as the central core. In the GTX 680M, 7 blocks are active leading to the 1344 CUDA cores. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are of similar speed to one shader of a Fermi chip (as the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

The graphics performance of the GeForce GTX 680M is on average above the Radeon HD 7970M, thus making the Nvidia card the fastest mobile graphics card as of summer 2012. The GPU has enough power to run demanding games of 2012 fluently with Full HD resolution and maxed out graphical settings. Only the extremely demanding title The Witcher 2 will not run fluently in ultra settings. Battlefield 3, Skyrim, and Crysis 2, for example, are playable at the highest detail settings.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK104 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENC API.

The power consumption of the GeForce GTX 680M should be similar to the GTX 580M and therefore best suited for large notebooks (17-inches or greater) and desktop replacements.