NVIDIA GeForce GTX 670MX SLI vs NVIDIA GeForce GTX 660M

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 660M

The NVIDIA GeForce GTX 660M is an upper mid-range, DirectX 11.1 compatible graphics card that was announced in the first quarter of 2012 for laptops. As of this writing, it is the fastest Kepler-based GPU built on the GK107 architecture and is manufactured in 28nm at TSMC. The graphics card uses a 128-Bit wide memory interface with GDDR5-VRAM.

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK107 Kepler core offers two shader blocks, called SMX, each with 192 shaders for a total of 384 shader cores that are clocked at the same speed as as the central core. 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 was 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

Thanks to the GDDR5-VRAM, the gaming performance of the GeForce GTX 660M is well ahead of the GT 650M DDR3 and on par with the AMD Radeon HD 6950M. Even the older high-end Fermi-GPU GTX 570M is only slightly faster. Therefore, current games as of 2012 run moderately well in 1080p resolution and high details. Only a few very demanding games, such as Metro 2033 or Crysis 2, may need reduced graphical settings for smoother gameplay.

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 GK107 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 660M should be best suited for notebooks 15-17 inches or greater.